And Trump will hammer Bernie on socialism and his honeymoon in the USSR. We will be treated to endless clips of him frolicking with Communists and what can he say? Bernie has far more baggage than Warren and at least Warren has accomplishments to tout. I also have not heard one Trumpist that wants Warren to face Trump.
Even if you want to deliberately ignore Bernie's impressive legislative record and status as 'Amendment King' as you apparently do, that he singlehandedly shifted the Overton Window in American politics to making discussion and support of singlepayer healthcare, free college, campaign finance reform, money in politics and UHC mainstream, while simultaneously reviving the FDR wing of the party, both things that would have been deemed unthinkable by the vast majority as recently as 2016, is by itself a historical accomplishment that trumps, pun unintended, anything Warren has done despite my immense respect for her. He has objectively set the tone and baseline for the Democratic party; this is beyond dispute; even if he loses the primary, he still wins.
Beyond that, if you legitimately think that ancient clips about his honeymoon to the USSR, and 'muh socialism' based attacks are going to be enough to sink his candidacy in the general, I don't know what to tell you other than that your innate bias against the man is clearly clouding your judgement. First of all, those clips have been in circulation for awhile, and they haven't really done much to blunt Bernie. Second, the line of attack is not really going to resonate with anyone outside of Trump's base, and Donnie already got that on lockdown. Few people care about Republican McCarthy hysterics anymore; they've played it to the bone after having unironically and repeatedly called Obama a communist and socialist; someone who is a centrist at best, even by American standards (and staunchly conservative anywhere else in the developed world:
Obama the Conservative | Tracking Obama's abandoning of the progressive agenda, and the disconnect between his words and deeds. ), meanwhile as good, popular policies, both existing and pending become associated with socialism per Bernie's deliberate maneuverings, it gets blunted even further. Bernie was playing actual 3-d chess in identifying as a democratic socialist despite obviously being a social democrat, knowing full and well that Repubs are ultimately going to come at him with this as their primary line of attack; this is a tactic known as 'getting out in front'. Now more than ever, it is exceedingly easy to frame such alarmism as the blatant absurdity it is. When you overuse and blanket everything left of Republican fanaticism as 'socialist/communist', as the GOP has done, you will find that the word is quickly robbed of its power of pejorative.
To be clear, I think Warren has a good shot in the general, and certainly a better one than Biden at this point who continues to deteriorate, but I find your basis for pearl clutching about Sanders is largely baseless in light of the facts as they stand.