I don't think Hillary wants to stay in the Senate. A lot of Senate work is boring. She has always wanted to be President, and her Senate seat was just the first step.
I suppose it can be. It would depend on the individual. If she is thinking for herself she can do a lot within the Senate and have influence far outside. If she is trying to be something she is not, she may find her position stifling. If winning the Presidency will validate her life for her and nothing else will do, then she may remain unvalidated.