I feel like when he killed himself god gave him a second chance to do it all over. Because of free will though it was all god was able or willing to do, reset and hope he makes better choices.
As for the devil I guess you could say he is in hell because his plans always fail after years of planning because god resets things therefore never allowing him to succeed.
He never deserved the second chance. The ''devil'' was right -- evil just set the stage, it didn't force Kevin to make his incredibly selfish decisions that lead to disaster. I used to watch this movie and be frightened by it every time it played on t.v as a kid and thought the devil and the demons were after Kevin and his wife. But watching this movie again as an adult I have a totally different take on it.
The evil stuff was just background noise rather than the real problem which was a self-centered and greedy man who would sell out his morals, his wife and whatever else to get ahead. He had many chances to make better decisions but he never did. Why should he get a second chance?