Here's the funny thing about expectations: where they begin don't necessarily indicate where they will end up. When Bernie Sanders announced his campaign for the Democratic presidential nomination a year ago, I didn't expect him to win the nomination. I thought it was possible, but not very: I think I estimated the probability of Sanders winning the nomination at about 2%. (I also estimated the probability of Donald Trump winning the Republican presidential nomination at about 2%, so what do I know?) But his stances appealed to me more than those of any other candidate, so I supported him from the beginning of his candidacy. If you told me a year ago Sanders would get 1,877 of the 2,383 delegates (with only 49 of those being superdelegates), I would be quite satisfied.
Then, of course, the campaigns actually played out, and it looked, at least for a time, that Sanders had a nontrivial chance of actually winning the nomination. Unfortunately (if you're a Bernie Sanders supporter), that time has effectively passed. While I'm loathe to cite the Associated Press, particularly because they prematurely declared Hillary Clinton the nominee—more on that later—if you search "democratic primary delegate count" in Google, it will tell you Hillary Clinton has netted 2,203 pledged delegates to Sanders's 1,828, crediting the AP as the source. The only primary remaining is the one in Washington, D.C. There are only 20 delegates available in that primary. which means Sanders needs at minimum the support of 535 of the 714 superdelegates, or 75%, if he is to clinch the nomination.
Technically speaking, it is possible that they vote him in such large numbers, despite the fact that 581 superdelegates have currently pledged to support Clinton. It is possible the superdelegates decide, individually or collectively, that Sanders is a better candidate to take on Trump. But the fact that Sanders is now dependent on their supports means he has already lost. From the beginning of his candidacy, Sanders promised a grassroots campaign. Further, he has criticized many of the superdelegates for potentially subverting the will of the people by publicly throwing their support behind Clinton before any votes were cast. Clinton has now won a majority of pledged delegates, which are determined by votes. Sanders could overcome this only if superdelegates vote for him in large enough numbers to overturn Hillary's pledged delegate majority, which truly would be subverting the will of the people. In other words, the only way Sanders can become the Democratic nominee by becoming a hypocrite.
This is not to say Sanders should feel particularly compelled to end his campaign before the Democratic National Convention. If he wants to influence the Democratic party platform—and I'd be hard-pressed to believe he doesn't, given he isn't even a Democrat yet campaigned for the Democratic nomination (and he has recently spoken of what he hopes to see in said platform)—the best way for him to do that is to continue to campaign. By doing so, he amplifies his voice beyond the reach of his social media platforms. Indeed, recent news articles seem to indicate Sanders remains in the campaign to maximize his influence. But if he was serious when he stated his intent for a grassroots campaign and a political revolution, then he can no longer actively pursue the nomination without reneging on that intent. I don't know how he'll continue to campaign as he does that, assuming it's possible to do so; but if he can't, he can no longer justify his candidacy.