I once ambushed a family member all by his lonesome and killed every member of his guard, only he escaped and retreated into a nearby city that I had actually been on my way to siege. I sieged the city and forgot about it when I was invaded from another direction. I went back to look several turns later and discovered that over a period of turns the family member's guard had been replenishing even while the garrison was losing men from the siege. Kinda lame.