I'm pretty sure he will, for various reasons. It costs something to return them, and doing so might be taken as ingratitude. He accepts them now, but doesn't solicit them in his speeches. As far as I know, he doesn't do mass mailers or contribution phone banks either.
He’s going to need money for the general. The media is controlling the message to the CLinton supporters.
I’m pretty sure you’re going to be looking at a Clinton/Sanders ticket.
Her camp is telling him to tone it down, because what he says will be used against them.