I've kind of wondered similar things. It seems unlikely it was planned from step one - from a perspective of "why" as it would seem to cause more damage than good than pursing the desired candidate from the inset (only scenario might be if they wanted to bypass vetting) - that said, Biden has never been their "ideal" guy in a voting contest with Trump. So I do think this opportunity is presented as a get-outta-Biden card that many in their party want to play - and slide in some yet-unnamed woman cheating the process again. (probably not Hillary).
I don't understand enough of the process to even begin to guess what happens next though. If he drops... do they just "default" all the votes to the presumptive VP? There's seems to be real risk of a last-minute shake up, but I don't have an earthly idea what to anticipate actually happening. The NBC interview was fairly light, and he didn't screw it up "as-bad" as Andrew, but I don't think it went well for him. If they find any evidence of a complaint of any type being made in paper, he's a cooked goose. And they might want to ditch him early in the process instead of having that liability show up now in October.
One thing I note is that he is VERY careful trying to avoid saying anything negative about Tara - I'm wondering if that isn't for sake of a risk of a defamation suit... which could open up the university files to discovery. There is public evidence the campaign staff went through those files right after these allegations first emerged, which doesn't help their argument for clamping them down now.