When I wrecked my car, the right front fender (opposite side of impact) had very very little damage (much less than damage pictured above), and they had to replace the entire fender. Im not sure if much could be done to repair that.
ive done quite a bit of metal work on car, and ive always beend told, and heard, if it aint wrecked or rusted dont replace it, if that was my car i would cut if somewhere a little past the gas cap, weld it, body work it, and then repaint the 1/4, and its a real B$&%h to get a whole 1/4 panel aligned right. and its way more work then needed in his case.
well i work at autobody shop i may not be a body man but IMO id say maybe replace its hit hard at bottom.also it looks crinkled .if not replaced will need alot of pulling and chance it dont rip it will have lots of bondo