Only for Bernie to capitulate to the scratched liberals.

As soon as the fix came in for Biden in 2020 there was no winning move. Bernie could have:

1. Split the party, guaranteeing a Trump victory, which would have immediately discredited whatever nascent left party Bernie created in the eyes of the people most likely to join (left-leaning libs, irregular voters who have any interest in winning). Democrats would have (correctly, seeing as Biden won) used this loss against the left for at least another generation. They would have imagined all the things Biden totally would have done instead of living with the reality of his actual presidency. What would have been the point? Or,
2. Given up like he did, which is a loss, but at least doesn't let Democrats credibly blame anything on the left, regardless of how the 2020 election turned out. A big reason none of the blame for Hillary's 2016 loss stuck to Bernie was that he campaigned for her after dropping out then.

It's hard to imagine what concessions he could have extracted from the party, because they knew he had no options but losing big by splitting or losing small by quitting. And of course the fix came in right as Covid hit, so any sort of "fight to the convention" strategy came with a real health risk.

There's a huge contradiction between describing how thoroughly the system is rigged for capital and ripping Bernie because if only he didn't give up he really could have done it. His campaigns still moved millions of people left, which is significant no matter what else the guy did.