Try getting a burrow on the dwarves and assign them to it.
Already tried that, but to no avail. I start to think, that some backstory is in order.
The story so far...
1. In Spring, goblin siege arrived. I locked the gate and set alarm.
2.Goblins pass through the Hall-o-Pain and get slaughtered by zombies captured from previous necro siege.
3.Zombies then escape confinement and flee off the map. I turned alarm off at this point.
4.Naturally, giblets cluttering Hall-o-Pain didn't get properly disposed of - dwarves slacked on cleaning.
5.Autumn brings another necro siege. One of the necros manages to slip inside before gates are closed. He then goes to Hall-o-Pain and raises all the rotten gobbo gibs.
6.Alarm is raised, militia comes to restore order. Necro is killed almost immediately.
7. Squad then proceeds to mop up undead giblets. One rotten Ngokang's head survives, and becomes invulnerable, it seems. No amount of bashing or hacking can bring it down.
8. Alert disabled. AND NOW all dwarves flood the hall-o-pain to pick up the trash. Next, they see the head, and everyone charges it.
9. After taking a month's worth of beating by 100 dwarves, Ngokang's head is still alive. I conclude it is invulnerable, and set alert to stop dwarves from collapsing due to exaustion.
10. Head managed to push 2 unconscious dwarves to death. The irony.
11. I order the hall-o-pain to be walled off. Additional burrow containmig stone is set, and mason assigned to it.
12. Hall-o-pain is isolated from the rest of the fort. I disable alarm. From now on, dwarves stop eating and drinking, though some still perform jobs.
13. Necro siege arrives. It brings some LIVE (!) goblins (not undead) along, and the entire mob of zombies just camps at the southern edge of the map.
Tested it once again and yes, It seems that dwarves are stuck in the last alert burrow state. I've created a burrow directly on top of the booze stockpile, set alert to it, then (after dwarves gathered there) disabled it. Yet, even with no alert dwarves still stood there, not moving an inch.
Damn, it was a nice fort. I even managed to trap a fire-breathing flying FB and build an incinerator around it. They say losing is fun, but in my case, it cannot be more grim.
P.S: Not all is lost. Some (very few) dwarves drink and eat! I counted 3. I will just call it natural selection and move on.