I'd bet there will be at least one debate. I can see Trump's team believing that if he can bully and dominate her in a debate, make her look weak, etc he can come out the victor. Embolden the base, impress/entertain the rest of the electorate. And after that he won't accept another debate, since such a move is unlikely to work again. It's a hail mary but it's probably the only one he has.
In reality I'd expect him to instead look like a fool in the debate, the media will continue turning on him, and the official message will be "the debate was rigged, the media is in the tank for Hillary, etc." After that he'll decide not to do anymore debates.