Ezra Klein has had some good content on this topic recently. He talks about how a new candidate might be agreed upon at the upcoming Democratic National Convention, and the positives and negatives that might result from that switch. The drama of it all would likely lead to increased political engagement, too.
It’s not too late. Imagine if Biden actually had a health crisis between now and November and had to drop out. No way would the Democratic party not galvanize to find a replacement.