Is it gone? I was able to glue my Mom's back together with decent results. Fender is ABS. ABS glue (plumbing stuff) works on it. That and some scrap ABS sheet for reinforcement was all I did. Just looks scratched or cracked now. Way better than flapping in the breeze.
Winnebago should be able to sell you one too. Just have your credit card ready...
(And, by the way, you're not the first person to have a fender issue.
Lot's of talk about it here.)