The parameters of the rest of the Democratic Primary season are a lot more clear now.
About two-thirds of the delegates remain to be allocated.
It takes 1,991 pledged delegates to have a clean majority win on the first ballot at the national convention. If Sanders got 1,991 delegates at any point in the primary season, Biden would concede and drop out of the race without forcing the issue to a vote. For this to happen, Sanders would need to win something like 55% to 57% of the post-Super Tuesday vote, depending on the final delegate counts.
There are three groups of delegates: delegates pledged to either Biden or Sanders, delegates pledged to someone who has dropped out of the race (or Gabbard), and superdelegates (who don't get to vote in the first round).
The final Super Tuesday delegate counts are not yet complete. Right now, Biden has a roughly 65 delegate lead over Sanders, but that gap should narrow as more delegates from California, Colorado and Utah, where most of the unallocated Super Tuesday delegates are and where Sanders had a strong lead over Biden.
A best estimate of the number of delegates pledged to someone who dropped out of the race, which won't increase for the reset of the campaign, is probably in the 300-400 range. A plurality will be a majority of the remaining delegates. So, a plurality will be a minimum of about 1791 to 1841 delegates, which is about 45%-46% of the delegates. Either Biden or Sanders is guaranteed to receive a plurality.
A plurality is going to be very close to a majority of the remaining two-thirds of delegates to be allocated, because the gap between Biden and Sanders after Super Tuesday is small, and because both Biden and Sanders are almost certain to meet the 15% threshold in almost every state and in almost every Congressional district in a two man race, and the delegates from each state will be allocated very nearly in proportion to the popular vote in each state going to Biden and Sanders respectively.
Sanders has announced that he will concede the race is Biden has a plurality going into the convention. This is wise. Assuming that Warren delegates support Sanders, that Buttigieg delegates are split, and that other delegates for candidates who have dropped out support Biden, which seems to be a fair prediction, the delegates for candidates who have dropped out will be very nearly evenly split between Sanders and Biden, but will slightly favor Biden. Conventional wisdom is that a majority of the superdelegates favor Biden. Certainly, a majority of superdelegates would back Biden is Biden won even a plurality of the pledged delegates. So, Sanders has really lost nothing by stating that he will concede the race if Biden has a plurality of the delegates going into the convention.
So, the first, and possibly subsequent rounds of voting at the national convention will be held only if Sanders has roughly 45%-49% of the delegates, and Biden has about 41%-44% of the delegates, falling behind by less than one percentage point to as much as eight percentage points.
It isn't perfectly clear that the superdelegates would overturn a plurality of pledged delegates win for Sanders, even if they could and would have been inclined to favor Biden by a sufficient margin. And, the larger the Sanders plurality, the more risky it is for the party for the superdelegates to hand the nomination to Biden.
If Sanders had 49% of the delegates and Biden had 41% of the delegates, and 60% of the delegates for candidates who dropped out favored Biden, leaving the total pledged delegate vote at 55% to 45%, the super delegates might be able to hand the nomination to Biden, but would risk a complete meltdown of the Democratic Party and active sabotage of Biden's general election candidacy, if they did. For this to happen, Sanders would need to win roughly 54% to 56% of the post-Super Tuesday vote.
On the other hand, if Sanders had 46% of the delegates, Biden had 44% of the delegates, and the 60% of he delegates for candidates who dropped out favored Biden, equally splitting the convention, and the superdelegates tipped the balance in favor of Biden then, the Democratic party and the Biden candidacy would still be hurt, but, perhaps, not badly enough to be so obviously catastrophic that the superdelegates would refrain from doing so. For this to happen, Sanders would need to win about 51%-52% of the post-Super Tuesday vote, depending upon the exact Super Tuesday delegate count.
Results in the uncertain range between a Biden plurality and a Sanders majority are quite likely. This is because the states where Biden is likely to be strongest, based upon past experience, have disproportionately already voted in either the South Carolina primary or on Super Tuesday. The remaining primary calendar tends to favor Sanders, so Sanders is likely to get a majority of the remaining delegates and hence, to win at least a plurality of the delegates.
But, given the consolidation of both the left leaning Sanders track, and the right leaning Biden track, in the race, now that everyone else has dropped out of the race, it will be quite challenging for Sanders to consistently get 57% of the remaining delegates, barring a really serious misstep by Biden that changes perceptions of the race - something that could happen in the next debate or elsewhere on the campaign trail.