Nah. Biden is in his basement because they are adjusting his circadian rhythm to avoid "sundowning" common in dementia patients. Basically, the reason he is not coming out in public is that they have him in a controlled environment where they are adjusting the light/dark cycle to trick his body into thinking it is morning instead of night when he debates. This way he will be at his best and not lose it like he normally would in the evening.

In addition to adjusting his circadian rhythm, they will also pump him full of anti-Alzheimer drugs and he will have a flesh colored earpiece that they will use to feed him answers. It is clever. And we should not underestimate how he will do at the debate.