Don't think 42.06 and 43.05 have any differences in reanimation. Hair will reanimate when partly or entirely from grasping limb or head.
With necro sieges, there are no big beasts, so if you're atomsmashing anyway can use live bait, door and repeating 10-long bridge (some undead will be able to cross if you don't lock the door in their face, FYI). You don't need to put this into the entrance of your fort, a separate corner elsewhere will work as well. Unless you dug out a whole layer and covered it in workshops, there is an available path somewhere.
Alternatively, if you want to keep their gear, replace the bridge by high-weight or high-speed minecart cyclotron/grinder.
Or you can use a retracting bridge instead and drop them into safekeeping, to be directed to fight goblins at your leisure or whatnot.
Quite a lot is possible when building destroyers or size isn't a concern.
That said, when I've done army vs FB combat, I've tried to set it up so with hatches that the moment FB enters into view they're in the striking range of many or all the attacking dwarves. This has killed, amongst others, a webber and fogger with no injuries (though my dwarves were really badass at the time, I think Legendary +80 weapon/fighter among the better ones). I'd try to apply the same to army, though not sure what order would be best to prevent charging ahead - I'd guess defend burrows?
But whether your army can succeed...Well, the primary question is if their weapons can get through zombie armors. Dwarven towers are the most reliable source of steel-armored enemies in game, which would mean that the edged part of your military should use adamantine (with things that work okay as blunt like morningstars exempted).
And yeah, they'll leave in a season or year if you do nothing.