Since the CSS surface is still intact, I would only be concerned about hitting a big bump, corrosion of the metal inside the hollow area where you can't see it, cracking at the spoke holes, or vandalism by a drunk (I recall seeing a row of bikes in a bike rack outside a bar, every rear wheel was taco'd).
In other words, why would it not last forever if you are careful with it? I think that the best comparison would be to a rim on a bike with disc brakes.
My CSS rims are used in winter where chemicals are used to de-ice road surfaces, so I suspect that corrosion will kill my rims before anything else will.