The problem with Biden is that he's going to lose to Trump. Voters' major concern about Biden was his age, and he completely validated those concerns last week. His polls are bad and getting worse, and we can't wait and see if they get better; we don't have that much time to waste. We need to replace him.
A contested convention is risky, but it's our best shot right now. It would dominate the news cycle for at least two weeks and create energy and excitement in the base. As long as we come out with someone generally inoffensive, we have a good shot of winning. My pick would be Gavin Newsom; I don't particularly like him, but he's polling on Biden without even campaigning.
It is now very unlikely that Biden will win the election. Acknowledging that isn't the problem, and ignoring it and hoping it goes away isn't the solution. We need to accept it and find a solution.