We do have example of Christ having to stay strong right up until the end, to fulfil all things, so that is the end of once saved always, because all had to be done, or nothing was done.
We do have one apostle to the Gentiles, apostle Paul, who said to follow him for he follows Christ, so again that is the end of once saved alwas, as the words are to follow as he follows Christ, which as all the world knows or heard, is to finish all the things the Father gave the Son to do.
Lastly to totally wipe out once saved off the face of the earth, is we do then have that same example of apostle Paul, who again, did complete things the same way, right up until the end, so there is plenty to speak about but no other examples to follow.
John 16:7 Nevertheless I tell 
you the truth; It is 
expedient for you that I go away: 
for if I go not away, the Comforter will not come unto 
you; but if I depart, I will send him unto 
you.
John 19:28 After this, Jesus knowing that all things were now accomplished, that the scripture might be fulfilled, 
saith, 
I thirst.
Acts 13:25 And as John 
fulfilled his course, he said, Whom think ye that I am? I am not he. But, behold, there cometh one after me, whose shoes of 
his feet I am not worthy to loose.
Acts 20:24 But none of these things move me, neither count I my life dear unto myself, so that I might 
finish my course 
with joy, and the ministry, which I have received of the Lord Jesus, to testify the gospel of the grace of God.
2 Timothy 4:3 For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears;
4 And they shall turn away their ears from the truth, and shall be turned unto fables.
5 But watch thou in all things, endure afflictions, do the work of an evangelist, make full proof of thy ministry.
6 For I am now ready to be offered, and the time of my departure is at hand.
7 I have fought a good fight, I have finished my course, I have kept the faith:
8 Henceforth there is laid up for me a crown of righteousness, which the Lord, the righteous judge, shall give me at that day: and not to me only, but unto all them also that love his appearing.