What do you call a subordinate clause that follows its main clause but is wrongly punctuated as a separate sentence?

“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?

This is one of the two great bugaboos of grade school English: a Sentence Fragment (the other being its near opposite, the run-on sentence).

The folks at that link argue that, while technically incorrect, it can be useful as a point of emphasis, but

the freedom to exercise this stylistic license depends on the circumstances. Perhaps your final research paper in English Composition is not the place to experiment

The link I posted seemes to suggest that when purposely done, this is a Stylistic Fragment. If you'd prefer a more pejorative term, frankly I'd just stick with "sentence fragment". Anything more elaborate simultaneously elevates the activity and removes it from a term the culprit is likely familiar with from grade school (and as a grown adult, should know better than to do).

If

This compelled the chancellor to shut down the whole program. Which was an outcome no one really wanted.

is incorrect, surely the reason is that the relative pronoun references the preceding noun group. And a program can't be an outcome.

Sentence fragments, used in moderation, are (as WS2 implies) nowadays not considered ungrammatical per se [Nordquist; ThoughtCo]. In fact, they can add dramatic emphasis.