.. aight, so I've got 167 goblins with various normal- and flying mounts outside my fortress, with a warmaster nonetheless.
.. needless to say, my military can't cope with that so I've dug myself in (pun intended).
The problem however is that they've been camping there around two seasons now, and I'm running quite low on supplies. Any knowledge on how long they will actually camp outside?
Not much longer, but they might troll you (pun intended) by retreating, then after a few minutes returning to keep siegeing you, or steamroll your dwarves if they got out of the fortress. But I don't really see how you can be running out of supplies, plump helmets will keep your population fed and drunk indefinitely, if you have a soil layer. Pig tails will give you unlimited plant cloth, the other two cloths are only needed for moods really. If you dig out a soil layer and breach (then wall off) a cavern, you'll have a secured underground tree farm.
But, if you already have the above, nothing really stops you from making a siege-killing goblinite harvesting trap. For example, a long underground corridor with your fort on one end.
^BWWWWWWWWWWWWWWWSSSSSSSSSSSSSSSSSSSSSSSSSSCCCCCCCCCCCCCCCCCCCCCCCSSDB your fort
B=lever-operated raising bridge, as many tiles as you want.
W=weapon trap. If it's not a spear or a menacing spike, throw it in.
S=upright spear or spike, all linked to one lever, that's placed where it can be pulled /R quickly (dining room).
C=cage trap
D=door,
not linked up. Close it to turn goblins around, their weapon masters are Matrix agents who run across trap corridors without injury, but ideally, the number of cages is sufficient to get them all.
^=up ramp breaching to the surface. Miner should be disposable, or quick
If the tunnel has turns in it, he can even survive bowgobbos.