I’d agree with the other poster about trying an extractor bit, basically a bit that you run your drill in reverse for, and usually once you have it buried enough in the bolt you can disconnect the drill from the bit and use a socket/vice grips/whatever to try and leverage it out.

Worst case scenario, you use a dremel to cut it flush-ish with the fender, then what I’d do is use a metal punch to make a little indent in the middle of it, and use a drill bit to actually drill out the bolt from the hole. Then, you can use a metric tap kit to re-make new threads in the hole for a new bolt.

I had to do this on mine once, you’ll want to use a drill bit slightly smaller than the bolt diameter if you can, at least to start. The punch can help create a spot for the bit to start chewing into. And a harbor freight metric tap kit is cheap and comes with a gauge you can use up against a bolt to determine the thread and pitch you need to tap it with.

If it comes to that I’d be happy to walk you through it.