To add to Hujiklo's priority-based idea, you can have a list of actions that an enemy wants to do. The list should be sorted in priority. This way, after the highest priority item is done, it automatically reverts back to what it was doing before it was interrupted. Of course, if it dies or something along the way, then the list of priorities should be deleted along with the character, so it will automatically cancel all other priorities instead of trying to revert back to patrolling after dying (for example).