Choose two target creatures controlled by different players. Return those creatures to their owners' hands.
If one of the two target creatures becomes an illegal target, Run Away Together can still determine its controller only to check whether the other creature is a legal target. If the illegal target has left the battlefield, use its last known information. If the other creature is still a legal target, it’s returned to its owner’s hand.
If both creatures are controlled by the same player as Run Away Together tries to resolve, both targets are illegal. The spell doesn’t resolve.