I'm thoroughly skeptical of this. As others have said, Trump doesn't like to lose. Resigning = losing. He'll have to be impeached.
Losses can be turned into wins with the generous application of alternative facts! If Trump decides to call it quits, he'll just hold a press conference at which he''ll declare that he has fulfilled all of his campaign promises, that he has accomplished more in one year than Obama did in eight, that his administration has been the most successful of all time, and that since he has accomplished what he came to the White House to do, he is leaving the country in the capable hands of Mike Pence.
