OK, let’s go with this.
This “someone” who made a deathbed conversion to Christianity, but he doesn’t die. He lives for many years, and he lives a good Christian life for awhile, lets say maybe a year.
But he falls away from the faith.
Something happens in his life, maybe he loses his job, or maybe his spouse.
He grows angry at God, and blames God at his situation.
He turn away from living a good holy life, and begins to sin, small sins at first, but they continue to grow in severity until finally he is living in adultly, or fornication. He is angry and resentful, finally he goes back to his old Job, because he has never been able to find a new job, and he wigs out, and kills several people at his old job place, and then turns the gun on him self and dies.
Is he still saved?