I've seen them last as long as 150K miles w/o a fluid change ever but I have no idea how aggressively that car was driven. I also know that they'll last longer than that with fluid flushes so that'd be adviseable and Volvo now advises that too but NOT in print for older models. It IS in print now for some newer models, notebly AWD cars.
There's one guy who use to frequent this board who use to (seemingly) almost bash anyone who'ld suggest the idea of fluid changes (flushes) and was trying to see how long he'd go w/o doing it BUT I have no idea why anyone would care to risk a $2,300 trans replacement (average estimate) vs a little minor and in-expensive preventative maintenance once in a while.