I'm confused by your question. Cobell took the candle from storage in Mark's basement. Casey used it at Lumon in Mark's therapy session. We now know why Cobell took that candle...well, at least partly....but not so much the motivation behind it. But the connection is there at least.
I'd say Casey is most def severed...whether she has an outtie is the question.
Hm, but was it the exact same candle, or just one made by the same company?
Also, what would the point of using it be? To establish if it would subconsciously trigger memory (thus the tree sculpture?). Ok, but it does seem a bit... convenient?

Cassey seemed to be afraid that Mark and Helley would die in the corridors, which might not be an inie thing to be (inconclusive there, imo).