I wouldn't bet on it, but SC will probably be Webb's best state unless he stays in until VA. It's certainly possible though. Maybe a 1/3 chance?
Edit: I think that African Americans that are disillusioned with Hillary will probably go for Sanders over Webb.
Agreed, though I have a feeling that African American voters will by and large stick to Clinton unless she is completely silent on the issues hurting their community, which is very, very unlikely. Webb will be second in SC, with less than 10% of the vote. Sanders will place second in the remaining states.