@snood,
Okay, put yourself in Bernie's place. You started out unknown against the candidate that the party leaders and everyone else said had it wrapped up. You do much, much better than anyone imagined. The Republicans push this Email business and the FBI gets involved. After looking it over, the FBI decides some rules of Emailing government documents were broken. The FBI says a few weeks ago that they are investigating and will tell you if they plan to seek an indictment in a few months. That would put that decision somewhere near the end of July or so.
If you're a candidate who gave it a good run, but looks like you're going to lose, are you going to throw in the towel and concede as long as there is any chance, however slight, that the FBI might decide to seek an indictment against your opponent before the convention? I wouldn't.
I personally don't think Hillary is going to face an indictment since the report said that the last five Secretaries of State also broke the rules. Don't forget, when Hillary was in high school computers were bigger than refrigerators and had vacuum tubes like the old TVs. Not vacuum tubes in the monitor, (there was no monitor anyway)-vacuum tubes in the electronic computing circuitry. Ditto for most of the people in her age group.
So coming down on them on Email and stuff is just a waste of time. But if I were Sanders, after all that work I put in, I would wait it out.