Maybe, the undead were not easy to take.
I played a lot of games in the near of mountain homes, towns or towers
the undead allways come in great numbers 80 + sometims withs necros (i had once 4 of them)
The necros might run away but the undead will stay, the siege can go for years (till all of them were killed)
The earliest siege i ever had was in the second year, the 1st dwarven caravan just left the map and they started the siege …. 78 undead against 11 dwarfs :-)
the undead don't wait till you reach an number like the goblins.
i also had once that one of my wardogs died (i don't know why) but he become an undead and run to the butchery …. and we had an lot of undeads ….
i also had once an ambush as the human caravan entered the map the guards killed 3 goblins, the goblins become undead and killed the humans and then they also become undead (this all happens before i had any undead siege or necro on my map, no idea how or why this happend)
Also some funny things : an undead siege startet about 80 undead, than an ambush of the goblins startet and the 7 goblins killed all the undead.
Playing in the near of the undead means allway to expect that an undead-epidemy rises somewere somehow, you need an good military if you would like to keep the traderouts open if not, its also possible to stay in the halls for years. But an neverending siege means there were no migrants or trade caravans (they tried but after they were all butched a few times they don't try it again). Even if you make it once to kill the undead still noone is coming to you home after it. I waited three years after a 6 year siege and noone visited me anymore.
But the nice thing is if you can survive with an good squad the guys will have hundreds of kills and all become legendery with they weapons. As I said if they survive long enought.
Oh and allways clean the map, bring every corpse inside or even better destroy it.