Bernie is still relevant
Following the decision of FBI Director James Comey not to recommend to the justice department that Hillary Clinton be indicted for her irresponsible handling of classified information, the last hope for Bernie Sanders to win the Democratic nomination has disappeared.
Should Sanders now accept his unsuccessful campaign as no longer relevant to the Democratic Party? No.
Sanders represents a faction of the electorate that is fed up with politics as usual, the kind of politics that Clinton clearly represents. Clinton still needs to win over a large portion of this faction to win the general election. She won't win over all of it, even with Sanders' endorsement.
Without his endorsement, Clinton will have difficulty getting most of the Sanders supporters to vote for her in November.
Sanders has a right to demand a public commitment by Clinton on some key issues, a commitment made in such a clear, unambiguous manner as to make it difficult to back out at a later date.