Do you know what is involved in "hammering" out dents in a collision and how the metal looks after? Also you may need to then fill some surface irregularities with a filler.

This is why Deloreans that got into accidents were usually painted.

Of course if you can easily replace an entire panel with a new one, this can be done. On cars the rear quarter panel cant be "replaced" like the front quarter panel which is just bolted on.