You will get a rebuilt transmission usually with 2 year/24,000 mile warranty. If they do not offer warranty check other places. I know the BMW dealerships offer the warranty.

while the word "rebuilt" might scare people, I have heard it is basically as good as new. You would pretty much be getting the same transmission. Nothing different about it so a failure will probably occur again. However, since most of the failures occur around 70k+ I would expect you would have gotten rid of the car by then.