You're not very familiar with the Epistles and Revelation. There are times when individuals reject God and He finally turns them over to their depravities.
Final impenitence can occur at the end of life. Until then, all can call on God's mercy and be sure of being heard. All can trust that God will give them the grace of conversion if they avail themselves of the helps provided by God (prayer, fasting, spiritual direction, avoiding occasions of sin, devout reception of the Sacraments).
Some people foolishly put off their conversion until the end. The problem is, people don't know when they're going to die. Some people die instantly. Some people, when they die, are so preoccupied with the temporal business of dying that they forget the need to be penitent. For some people, the pride dies 25 minutes after the heart stops beating. There are very few deathbed conversions.