The debate is inconsequential, the point is, Trump is controlling the dialogue. This debate may or may not happen but it’s going to be on Trumps terms.
Yes, Trump is controlling the dialogue. Trump is dictating the narrative. In this case, Trump is demonstrating how to instill fear, uncertainty, and doubt (FUD) in his rivals, Hillary, Sanders, Obama, and the MSM, and play them off of each other— keeping them scrambling to catch up to him, keeping them off-balance, keeping them putting time and effort into trying to anticipate his next move— and then changing direction, throwing his rivals off-course.
I also think Trump could change his mind, come back and offer to debate. Sanders would look worse if he were to refuse, and now he has to hedge his bets by practicing for a debate with Trump which may never come, or take a risk that Trump is bluffing, and not prepare for a debate that might be offered by Trump later.
Right at the moment, Hillary is reeling from the State IG email report, and another cardinal rule is not to get in the way of an enemy destroying itself. if Trump hogs the headlines with a debate, then the news media could have used it as an excuse not to cover Hillary’s state department email problems.
(JMHO)