Others will know more than me on this topic. However they can wear and seize. Also a friend who has wrecked a few Suds and 33's has found some plastic bearing carriers melted!
My Sachs clutch was only about 30,000k old but had the "fingers" on the backing plate half worn through.

Which is the way they often go, but not that soon (no I don't leave my foot on the clutch). The bearing was perfect though. That is why I need to check the hydraulics!
Another fact I learned is that you can get (or brakeplaces can) individual parts etc. The backing plate was 150 but by the time you added the price of the bearing carrier it was worth getting the whole thing.
One more point.Th back of the bearing carrier has a slightly raised section where it fits round the shaft. This very slightly fouls the fingers on the clutch release arm. w are going to modify that slightly but it's not a big deal.
regards
paolo