Biden's biggest fundamental problem is that if the press is fully resolved to disqualify him on unfair, ableist grounds, that's just as immovable as his refusal to quit.
In Wisconsin today he explicitly said it would be anti-democratic for him to quit when so many had voted for him. I think that's exactly right, and don't think he'll be moveable if he views those as the stakes.
And they actually can't do it. Party leaders can privately or even publicly call for him to step down, but they probably can't prevent his nomination at the convention. (And if they did, it would be the biggest kamikaze move in political history.)