Bernie Sanders always seemed highly unlikely to win the nomination — and coming in far behind Hillary Clinton in South Carolina has reinforced that impression. But that doesn’t mean he will reach that conclusion and get out of the race; it doesn’t even mean he will fail to win future primaries.
I suspect that he got into the race without any serious expectation that he would win the nomination. He’s a cause candidate. He may have briefly started to think he could win, as the polls turned and he won New Hampshire. But since he didn’t get into the race with that expectation, he is unlikely to get out of it now that his chances look worse. He’s not going to drop out now in order to angle for a cabinet post in a Clinton administration; he’s not going to drop out to protect a reputation for pragmatism that he doesn’t have in the first place. So he’s going to remain an irritant for Clinton going forward.