I'd be tempted to do some Bondo magic on that. I always found it easier to sculpt spots like that from body putty to get the lines to be right again. Worst case you can always grind it back out easily and try a patch if you can't get it right. I would be inclined to do a large quarter panel section if I was going to replace the sheet metal. It's hard to get the body creases to line up right with a small patch in the corner like that.