At end of combat, you may exchange control of target creature you control that dealt combat damage to a player this combat and target creature that player controls. Whenever you roll , gain control of target creature you own.
Official Rulings for Glen Elendra
6/1/2012 : If either target is no longer on the battlefield or is otherwise an illegal target when the chaos ability resolves, the exchange won't happen. No creatures will change controllers. If both targets are illegal, the ability will be countered.