Take several isolated verses from all over the Bible slam them together irrespective of their context. 1 Cor 3:13-15 has absolutely nothing to do with all mankind's eternal fate.
13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
14 If any man's work abide which he hath built thereupon, he shall receive a reward.
15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
That says "every man", not "every saint", not "every believer", not "every church member", not "every Christian", not "everyone of us", and not "every labourer", etc.
(15) If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
(16) Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
(17) If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
Compare the destruction of v.17 to the destruction for salvation here:
1 Cor. 5:4 In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ,
1 Cor. 5:5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
So one who is destroyed & unsaved (3:17; 5:5) will still be saved (3:15).
Verse 17 of the context immediately following v.15 explains who those (lost ones) are that shall be saved:
(15) If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
(16) Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
(17) If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
Compare:
1 Cor. 5:4 In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ,
1 Cor. 5:5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
And therefore, in context, 3:15 is also referring to those who are not saved, but become saved "as by fire".
Therefore 3:15 can & does refer to unsaved persons getting saved. The most immediate context proves it.
You ignore the context Paul is talking to Christians at Corinth "labourers together with God: God's husbandry, God's building" not all mankind. You need to find a proof text which clearly refers to all mankind and not a certain group.
You overlook the immediate context which refers to those who are unsaved (v.17a):
(15) If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
(16) Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
(17) If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
Compare these verses, which also speaks of God destroying [albeit indirectly] an unsaved person, by giving him to Satan, in order to save him:
1 Cor. 5:4 In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ,
1 Cor. 5:5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
And therefore, in context, 3:15 is also referring to those who are not saved, but become saved "as by fire".
Therefore 3:15 can & does refer to unsaved persons. The most immediate context proves it.
Verse 11 says that "no one" can lay any foundation other than the one that has been laid which is Jesus Christ. The words "no one" are not limited to the saints in Corinth,
but refer to all mankind. This is the last reference identifying any group of people in the next several verses leading up to v.15. Thus prior context and the more immediate
following context both support the view that v.15 refers to the unsaved being saved.
Verses 16-17 of the context immediately following v.15 speaks of those who are not saved in 17a:
(15) If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
(16) Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
(17) If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
Compare:
1 Cor.5:5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
And therefore, in context, 3:15 is also referring to those who are not saved, but become saved "as by fire".
Therefore 1 Cor.3:15 supports Scriptural Universalism, that all will be saved.
Christ is the foundation for the entire world, not just believers. He died for all.
He is the light that lighteth every one (John 1:9)
How they respond to Him determines how they are building on the foundation.
Some build with gold, silver & precious stones. Others build with wood hay & stubble:
"Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;" (1 Corinthians 3:12)
Silver indicates the redemption of Christ. Those who build with silver, build with faith in Christ as their redeemer. They are believers.
Those who build with wood, hay & stubble build with things that will be destroyed by fire since they are not works of faith, but works of iniquity:
Matthew 7:22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? 23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
Their sinful works will be burned up, yet they will be saved, yet as by fire:
1 Corinthians 3:13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is. 14 If any man's work abide which he hath built thereupon, he shall receive a reward. 15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
1 Corinthians 3:15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
16 Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
The one who is destroyed (v.17) refers back to the one who "shall suffer loss: but he himself shall be saved; yet so as by fire" (v.15). Verse 17 explains
verse 15 of the immediate context. Similarly, in chapter 5, we have one destroyed in order for him to be saved:
1 Corinthians 5:4 In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ,
5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
1 Corinthians 3:16 Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
Jesus is the Light that lightens every man (Jn.1:9). Human beings were made in God's image & likeness. They are temples made by God:
Acts 17:22 Then Paul stood in the midst of Mars' hill, and said, Ye men of Athens...
24...[the] Lord of heaven and earth, dwelleth not in temples made with hands;...25...
he giveth to all life, and breath, and all things;... 28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring. 29 Forasmuch then as we are the offspring of God...
1 Corinthians 3:12 Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;
13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
14 If any man's work abide which he hath built thereupon, he shall receive a reward.
15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
Compare:
And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be. (Revelation 22:12, KJV)
And lo, I come quickly, and my reward is with me, to render to each as his work shall be; (Rev.22:12, YLT)
Jeremiah 17:10
"I, the LORD, search the heart, I test the mind, Even to give to each man according to his ways, According to the results of his deeds.
Matthew 16:27
For the Son of Man will come in His Father's glory with His angels, and then He will repay each one according to what he has done.
Revelation 2:23
Then I will strike her children dead, and all the churches will know that I am the One who searches minds and hearts, and I will repay each of you according to your deeds.
Romans 2:6-11 Who will render to every man according to his deeds…
In Mt 25:31-46...the righteous & the unrighteous are distinguished by their works.
James says faith without works is dead:
James 2:20b-26 faith without works is dead 21 Was not Abraham our father justified by works, when he had offered Isaac his son upon the altar? 22 Seest thou how faith wrought with his works, and by works was faith made perfect? 23 And the scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God. 24 Ye see then how that by works a man is justified, and not by faith only. 25 Likewise also was not Rahab the harlot justified by works, when she had received the messengers, and had sent them out another way? 26 For as the body without the spirit is dead, so faith without works is dead also.
1 Cor.13:2 If I have the gift of prophecy, and know all mysteries and all knowledge; and if I have all faith, so as to remove mountains, but do not have love, I am nothing...
4 Love is patient, love is kind and is not jealous; love does not brag and is not arrogant, 5 does not act unbecomingly; it does not seek its own, is not provoked, does not take into account a wrong suffered, 6 does not rejoice in unrighteousness, but rejoices with the truth; 7 bears all things, believes all things, hopes all things, endures all things.
8 Love never fails; but if there are gifts of prophecy, they will be done away; if there are tongues, they will cease; if there is knowledge, it will be done away. 9 For we know in part and we prophesy in part; 10 but when the perfect comes, the partial will be done away...
13 But now faith, hope, love, abide these three; but the greatest of these is love.
1 Corinthians 15:22 For as in Adam all die, even so in Christ shall all be made alive... 28 And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
https://www.tentmaker.org/books/hope_beyond_hell.pdf