As long as the metal is not kinked or the paint cracked, it should be removable.
BUT... I had a small dent on top of my front fender and I went to several local paintless dent removers here in St. Louis area. This was just after a big hail storm and there were many of them, usually setup in dealership parking lots.
None of them would do the front fender because it was a bike fender. I thought it would be quite easy for them to just roll off the tire with their tools and it's done, but they refused.
I made a tool out of 1/2" round rod with a slight spoon end. I ground it round on one side and then polished the end. With the right bend in it and the bike on the center lift, I was able to feel on top when my tool we in the correct place. I then just rocked the tire back and forth with the tool resting on the tire. With about a half dozen back and forth, the dent was gone and not mark shown.
I'm not saying this could be done with your back fender dent, but it may be worth looking into if you cannot get a local paintless dent guy to help you out.