I cncountered this once :  My buddy and I were on our way down after an all day ride in high alpine territory Co.  Came around a corner and my buddy slammed straight into a rock face after skidding off his line.  The front rim potato-chipped.  It was almost bent in half.  No problem I said to my buddy Ed : I should be able to fix it.  ...I grabbed the wheel, gave it a good look to distinguish the exact point that I should work my magic :  Hoisted the wheel above my head, and slammed it down onto a dirt muff and presto : the wheel re-acquired it's precise shape.  My buddy still talks about this.  Saved us from an 8 mile walk-out back to our cars.  Carbon would have broke.  Only aluminum can be fixed like this on-trail.  Still---I myself ride carbon now....