I'm not sure what you mean here...If the father had passed away while the son was off living a profligate life, the Prodigal would still have been his father's son and vice versa. Death does not undo this kind of relationship. Now, as I said, if what you propose had happened, if the father had died without reconciling with his son, there would have been no opportunity for the restoration of their fellowship one to the other but their relationship to each other as father and son would not have altered.
But, you see, what you've written here puts the onus upon the believer to sustain their salvation. Basically, it is works salvation. If I don't act to preserve my "alignment" with God, then I will die a lost man. How does this not amount to being saved by my efforts rather than the finished, perfect work of Christ on the cross?
I suppose. But the Bible never uses such an analogy to talk about salvation. The Bible talks about adoption, about justification, and redemption, and reconciliation but never does Scripture equate our being saved with being married.
But this is quite unlike what Scripture says is the case when God saves us. We aren't, before God saves us, a bride He has chosen to wed. We are walking corpses spiritually, dead in trespasses and sins, (Eph. 2:1) without the capacity even to desire to be saved. Unless and until God acts to redeem us, we remain in this state of spiritual deadness. There is no initiative we take toward God that He hasn't motivated in us. Our salvation is all His doing. A rather different situation than that of a bride and groom about to marry.
And, again, what you're describing here is, essentially, works salvation which the Bible flatly and explicitly rejects.
Titus 3:5-7
5 not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit,
6 whom He poured out on us abundantly through Jesus Christ our Savior,
7 that having been justified by His grace we should become heirs according to the hope of eternal life.
Well, what the RC church believed is rather contradicted by Scripture which tells us we can know (and must know) we are saved before we arrive at the Judgment Seat of Christ.
2 Corinthians 13:5
5 Examine yourselves as to whether you are in the faith. Test yourselves. Do you not know yourselves, that Jesus Christ is in you?...
1 John 5:11-13
11 And this is the testimony: that God has given us eternal life, and this life is in His Son.
12 He who has the Son has life; he who does not have the Son of God does not have life.
13 These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God.
John 5:24
24 "Most assuredly, I say to you, he who hears My word and believes in Him who sent Me has everlasting life, and shall not come into judgment, but has passed from death into life.
1 John 3:14
14 We know that we have passed from death to life, because we love the brethren. He who does not love his brother abides in death.
Selah.