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what do you think happened to Umbra?!?!? :/
The entire TES book deals with what happened to Umbra.
Go read it.
This is based on the games, seeing as the books are more of a secondary thing.
Too bad the book is official canon, and thus, it happens. The only thing not mentioned is how Umbra got back to CV, but artifacts like Umbra do tend to suddenly disappear without a reason. As such, either the CoC gave it to CV, or Umbra simply left the CoC/anyone who had it at the time.
As for whether it'll be in Skyrim, I really hope not. It's just an artifact, like all other artifacts, only black with a soul trap. Then again, it entirely depends on what happens to Umbra at the end of the second TES book.