I agree if Clinton gets a bump in the polls her lead could dissipate before November and that future debates will play a factor. I’m not saying Clinton will win if she moves ahead of Trump in the next week or two, just that she will likely lose if she can’t show some positive movement from Trump’s disastrous performance last night.
There is a reason Trump said that "[He] could shoot somebody, and [he] wouldn't lose voters." I've largely feared what you're saying. I don't understand how people can even claim to be mulling over Trump's "policies." What the hell is Trump going to do that will surprise them positively? Most people who are voting for Trump know exactly who he is. I think the debates will do nothing for Trump either way. I think your insight is right on, and if voters aren't even open to Clinton, the unthinkable will happen.