This article is from the ER FAQ, by Rose Cooper email@example.com with numerous contributions by others.
The short answer is: We don`t know.
My own personal prediction is: Probably not.
Sherry left the show in 1996 for a variety of reasons, one
of which was that she wanted to spend more time with her boyfriend.
She and said boyfriend have since split amicably, prompting much
speculation that Sherry may now be "free" to return. Such reasoning
overlooks a couple of things:
One is that Sherry`s agreement with the producers involved
extracting her from her contract with "ER". In return, she is
legally obligated to stay off of television for the remainder of
that contract, which would conclude sometime around the end of 1998.
While it`s possible that she and the show`s producers may find some
way for her to slide out of that obligation, just as they did for
her to slide out of her contract in the first place, I don`t like
to bet on lightning striking twice in the same place.
Another thing to keep in mind is that Sherry`s boyfriend
was far from the only thing that motivated her to leave "ER".
She was getting exhausted and stressed-out due to the rigors of
the show`s grueling shooting schedule, and apparently was even
beginning to question whether or not she wanted to work in
television at all. She was *so* willing to leave, that she and
the producers went to these extraordinary measures to get her
out of the show. It`s unlikely then, in my view, that she will want
to hurriedly reverse such a carefully thought-out decision.
-(Information courtesy Scott Hollifield).