LATEST UPDATE:
Sanders has 885 delegates
Biden has 1180 delegates
Biden wins Florida, Illinois and Arizona and with a huge lead it appears he will be reaching the 1991 delegates number first if the race continued.
Sanders is facing calls for him to drop out to give Biden the chance to start working on the November Presidential elections preparation now.
This is literally the end of this. Biden is going to win (bar some sort of illness, major scandal, etc) The only reason I see Sanders staying in is to be able to get something out of the administration, or to get Biden to change certain policies that he'll implement and he can tell his supporters he did something.
Sanders (IMO) is a little too old to be running for President again, so this is probably his last chance. He probably is hoping for some sort of extraordinary circumstances to help him out here. Or a cabinet role, like I said before. VP is off the table, as Biden has said that HE WILL pick a woman to be his VP.