Merc Return Button Gone

[tknarr]

That sounds like the merc was still alive and up, just not where you could see them (rendering problem, or they've run off somewhere and are taking their time coming back). There's nothing in the UI that can fix that. My usual fix is to use the green Peace button to recall the merc to me. If that fails, I use the merc window to suspend the merc, wait the 2 minutes and bring it back. That usually clears up any rendering problems and gets the merc back with me.