"It is a Christian fiction book that came out in the 90s.  The plot deals with, I think, three atheist who are shown by Jesus and Satan themselves, that they are very real, and they are free to choose between either of them when presented with a life they can have with either of them.  At the end of the book, they make their choices, and the big reveal is that all three are on their deathbeds, having had a stroke, heart attack, and I think a car accident.  After making their choices, they immediately die.  I want to say it is a Frank E. Peretti book, but looking at his list of books doesn't ring a bell.  

I'm drawing a blank here.  How about you?"