Something which has happened to me a few times already, and which could be fairly easily fixed/prevented:

In combat, an enemy decides to try to flank me and takes a long path around, but either due to an error in pathing or AI, the NPC manages to get stuck in a position where it can't continue forward. Unfortunately, there is currently no combat timeout for NPCs. So the game waits patiently until the NPCs move is completed... which never happens. At this point, the only option is to reload a saved game and hope that you didn't lose too much progress in the game because you cannot leave combat, and you cannot go find this "lost sheep" and kill it because it will never get back around to your turn again.

Simple solution: Combat timeout. The NPC can never be "AFK", so there is never a reason for its turn to take more than a certain amount of time. I'm not sure what a reasonable limit might be, but I wouldn't mind waiting a minute or two if I knew that I wasn't going to have to reload and lose potentially the entire level of the current mission (assuming autosave is still turned on) or several hours (if someone turns the autosave option off). So then, if the NPC hasn't completed its move in 90-120 seconds, the turn times-out and the combat continues with whomever is next in the initiative list, leaving me the option to go find out where this lost sheep is stuck and eliminate it.

You might even consider having this timeout have a health cost to the NPC so that if the NPC is hopelessly stuck and (worst case scenario - in an area that the player cannot reach), they will only timeout a limited number of times before they eventually die off, allowing the combat to close without forcing the player to reload a previous save.