I totally agree that parents must have realistic expectations, and some do but some don't. For example, on a parent's list I know of a mother who is about to implant her 6 year old, profoundly deaf since birth, son. Ok, that's fine, but realistically, he will NEVER become an oral language user, and chances are, he will become a non-user. They missed the window.
BUT, on the other hand, realistic view for a child implanted at 9 months would include being completely age appropriate with language before age 3, attending mainstream schools, hearing in the "normal range" and being able to learn and understand through listening only.
Oh, and if an implant fails, the vast majority of people are re-implanted in days. The child wouldn't be "thrust into" anything.