The most obvious possibility is AOC. In that case I am sure she'll move even further right and get totally ratfucked by the party regardless. That's the most jokerified option, I think. At the very least, her obvious ratfucking will push many more people to the left like the Bernie campaigns did.
But the worst possibility is some rando Democratic apparatchik we've never heard of like Mayo Pete showing up. They take up all the aesthetics of Bernie's campaigns, they receive the glowing endorsements of Bernie and the squad, but they seemingly refuse to outright promise anything we would call "good", and they suspiciously receive no material push-back whatsoever from the Democratic party establishment other than some clearly bad faith grumblings about how spooky and radical this person is. Win or lose, they completely suck the energy out of leftist movements in the imperial core for a further decade.
Not to defend any of bernies actions for the past few years but a big reason Bernie got such a following is there were videos of him saying the same stuff back in the 80s. He got whittled down and ground out by the DNC but he was relatively progressive for a time with consistent messaging that resonated with people.
AOC seems to be doing a speed run of Pelosi's legacy and you can already make a compilation of her saying something progressive and then weepily explaining why she had to vote for the opposite of that along with the rest of the parry.
Not only is there not anybody even close to bernies previously stated beliefs, people are gonna be less likely to enthusiastically support them after getting burned last time around.