If he doesn't show up, he will have "won" by taking the higher road, by not engaging or legitimizing someone the left has made out to be such a bad guy, or some similar rationalization.
Even if Biden does show up and merely drools on himself and mumbles for an hour (a not-out-of-the-question possibility given his apparent rapid mental decline) the MSM will declare Biden the winner.
I would bet you a good steak dinner the MSM is already writing/editing their stories for how well Biden "won."
If I were Joe Biden, I'd take that bet because..well..I'm Joe Biden. LOL
The "debate" is and has been in full swing for weeks, if not months already, in the public eyes and in the enemedia eyes. Expectations are now so low, if he does indeed show up and manages to keep his drooling below a certain amount, and limits gaffe-ing for a mere n times (n<5, say), he will have fulfilled the limited low expectations.
OTOH, the expectations are extremely high for Trump to clobber joe.
I'm expecting a Joe mini disaster and complete Trump triumph on Tuesday, to the extent Joe is declared the winner.