Definitely not warranted in this circumstance. And the carwash will probably have warning notices. You should never ever drive through one with an exposed antenna, even a fin type one, and should also fold your door mirrors in. Preferably never use them at all because many of them scratch the paint.

If this had left a hole in the roof or any wiring exposed, best to seal it up with duct tape. The dealer wants a lot of money for the repair, so might make sense to check out some independent car audio fitters to see if they can offer a cheaper fix. If you retrieved the fin maybe it can be patched up.