“This compelled the chancellor to shut down the whole program. Which was an outcome no one really wanted.”
I suspect that what underlies this error is the sense that in spoken English a substantial pause (or even a change of speaker in conversation) might well precede the subordinator. If this suspicion is correct, then the correction most true to the writer’s intention would be to combine the two sentences into one, perhaps with a dash instead of just a comma, rather than to edit the second sentence into independence (here, by substituting “This” for “Which”).
I find this sort of thing lamentably common in student writing lately, and have accordingly felt the need of a term for it. The term I came up with is “continuation fragment”—that is, a continuation of the preceding sentence wrongly punctuated as a separate sentence. Is there, however, a more established or usual term?