Guys, I'm a bit of a lurker here, but I got to say, reclaiming IS worth it if it's not too bad. if it is, go in adventure mode with 20 followers or so and clear it out. the cleaning up is bad, sure, and it may not be worth it if the fort is too big. but if you lost it in the first 2-3 years, which happens a lot to me, then reclaiming it could actually work. Three of my best forts ever were reclaims of forts that died out right before they were about to really take off.
I recall one fort I had that was re-embarked not once, BUT TWICE. Eventually it was overrun by two or three forgotten beasts, and it killed a ton of adventureres and dwarf military teams before they were eventually slain. Every once in a while I'd go for it, but it felt like it added to the lore. Once I visited it 20 years later after it's last abandon, and by golly, I wouldn't reclaim it then it was so run-down, but that doesn't mean I wouldn't do so otherwise.
Also use advanced world gen parameters and set embark points to max so you can bring better gear for these kinds of situations.
I reclaimed a fort that fell to a zombie siege. 4 embarks slaughtered by zombies, berserk miners and ghosts later, I finally got a foothold.
Then more necromancers came. Hundreds of bodies outside. Years of being trapped underground by endless hordes of zombies. It's a miracle that we survived. We thrived and created a military that could fight tens, hundreds of zombies! Nothing would stop them!
Then some workers and babies were killed in the caverns. TANTRUM SPIRAL.
Wow... epic.
However a baby/cat dup hold a special place in my heart for managing to survive a fightwith the FB , injuring it, then crawl off wounded to hide.
Epic as well.
But I can't find any pleasure in the new version of DF reclamation, with the lack of manpower and supplies to overcome the combined forces of all of the enemies on the map when you left, including ones that could not have gotten into the fortress without teleporting. Being forced to fight three FBs at once, with seven barely trained and ill-equipped Dwarves, just smacks of punishment for not having played the game according to someone else's plan.
A legendary adventurer backed up by 20-30 soldiers might do the job though, let your men take the brunt while you go from behind. Kill, rinse, repeat. Leave, retire, then reclaim.