To a large degree, that will depend on whether the claims are even somewhat substantiated. As of now, Reade's credibility is pretty bad.
The story is being reported mostly in right-wing media (where, of course, it's being trumpeted). Unless there's enough "there" there that the rest of major media focus on it at length, then I don't think it will have all that much impact - because the people that opt for Fox News are basically already lost to Biden.
As for Biden - no, not my first choice, nor my second (or third, if you get down to it). But that's really no longer relevant. I get to choose between Joe Biden and Donald Trump. To me, that is a no-brainer.
In my opinion, anybody who was considering not voting for Donald Trump (and that's pretty much everybody who's not in Trump's "base"), but who now decides to vote for Trump instead of Biden, is kidding either themselves or the rest of us. Even if Tara Reade's allegations are true - which is far from clear - they frankly pale in comparison to the allegations of Donald Trump's dozen or so actual rapes. That's leaving aside Trump's inexcusable dragging his feet on COVID-19, his attempts to shift blame for his own incompetence (to China, to the World Health Organization, to Obama, etc., etc., etc.); that's leaving aside his abject ongoing corruption funneling public money into the Trump Organization; That's leaving aside his attempt to extort the Ukranian government, and now his attempts to extort things from Governors in return for assistance - in return for actually doing his job.
Again IMO, if somebody says they were going to vote for the Democrat, but now can't, because blah blah blah, and instead will vote for Trump... well, they were going to vote for Trump all along, and were just waiting for something they could use to justify that.
We just have to hope there aren't too many such closet Trumpists out there, because it's not clear that our Republic will survive another four years of Trumpism. Today it was the neo-Nazis in Michigan who Trump encouraged as "fine people." Tomorrow? When somebody actually starts shooting? Ammon Bundy? I mean, if these people actually try armed rebellion, we'll put them down, because we outnumber them (and the right doesn't have a monopoly on firearms), but I'm not at all sure that our governmental institutions will survive that. Trump has done a lot of erosive damage already; at some point, the institutions themselves lose credibility.
If somebody wants to vote for that... well, that's their prerogative, of course. I just hope that those who make that choice live long enough to experience the results.