I have revised the wording of the Save mechanic to reflect the fact that the action cannot be refreshed until the effect has been used. I've also given users the ability to manually dismiss a Save before that happens:
Save
The action allows the affected character to return to the user if he or she becomes mortally wounded. The next time the affected character is reduced to zero health, he or she goes out of play, returns to the user, and goes back into play. The action may not be refreshed until either the effect is used or the user dismisses it by touching the affected character and declaring, "End Save." The effect otherwise persists until used.