Forever After — Gilbert M. Stack

Middle class, average-Joe, Paul Steele dies minutes after a terrible argument with his wife-dies, but doesn't quite depart for the world beyond. Instead he wakes in the body of billionaire energy magnate, Griffon Knight, and no one-not even Paul's wife, Char-will believe he's come back from the dead to be with her again. Trying to convince her only succeeds in making her think he's crazy. But no one knows Char as well as Paul does and he's not going to quit until he wins her back and convinces her to marry him again.