LOL
So I actually was able to reclaim the fortress, but not quite as I wanted to:
I loaded my wagon with booze, wood and some food, seeds and bars (though I took a pick to make things faster).
I took 3 skilled miners, a soldier, a mason/mechanic, a brewer/grower/carpenter and an armorer/weaponsmith.
I immediately dug in on a new area of the map and went into the caverns. Before digging all the way, I dug up a temp storage area, and while the miners and the soldier dug, I the other 3 butchered and processed one of the wagon yaks and built some doors. I sealed myself in and went into the caves. Rushing before any monsters attacked, we claimed a chunk of the caverns by means of double-thick obsidian walls. But before that, and just as my dwarves finished the store and began moving the food and alcohol, a snow storm arrived. I didn't know it was possible, but the storm actually destroyed my wagon and all of the stuff in it, which posed me a new challenge: although I had bypassed completely the 4-5 goblins remaining on my old fortress, I now had some 15 units of food and 30 of alcohol. Fortunately, a seeds barrel or bag was saved (I had 10+ plump helmet spawns).
Immediately we set on sealing off our cavern and growing some food. But the 80 units of wood I had brought were lost in the storm: I had only 5 beds and was able to craft 5 barrels, which my dwarves filled with the yak products. The 6-10 fungiwood trees there were rapidly turned into 3 more beds and some barrels, but even though I set up to reserve some barrels, all of them were readily filled with foodstuff. Oh well.
Migrants arrived twice while all this took place (a 3-dwarf wave and a 9-dwarf wave). I turned down the traders cos I was trying to solve the Booze Crisis. 3 dwarves refused to dishonor themselves and drink water, and actually died of thirst (a mason, a miner and the much-needed armorer/weaponsmith). I dug up a well, and while the production of food is growing, I've barely enough to sustain the base. This would be the right time for some goblins to ambush or something!
Still, the fortress has a thriving gold industry (no hematite so far, but I know it's our there) and we've dug up some neat obsidian halls and rooms. The last migrants were draften into the military for being completely useless (fish dissectors, animal trainers, pressers, woodcrafters, shearers and such, I mean what are they thinking: "Gee, I'm a beekeeper, lets head into the wild glaciers, where surely honey bee hives must be found by the dozen!").