Why in hell would he willingly drop out?
1. He just doesn't have it in him and I think he knows it (hence all the smoke signals for help, in the form of atrocious behavior)
2. Because he can extract a pound of flesh from the GOP and its donors (Koch brothers, how would you like to fund a major development in NYC? )
3. Because he is genuinely afraid that if he continues to run (and fails), he would be aggressively sued, blacklisted and destroyed.
I disagree with this logic. I think Trump would rather lose, claim the election was rigged (as he is already claiming it will be), and hold on to his most slavishly devoted loyalists by fighting to the bitter end, than drop out and risk losing his cult-like following. His brand is already irreparably damaged with the broader public, his best remaining option is to continue carving out a niche for himself on the far right.