In a new fortress that hasn't seen its first winter yet, I focused on creating defenses. My fort is built at the fort of a mountain so with a little slope removal, channeling, and a standard drawbridge, and a few traps I managed to make my fortress practically unapproachable on foot. After that, I used a channel to siphon water from a river into a cistern. I even made my dwarves remove all the stuff my miners dug up from the channeling so that nothing would be caught underwater. So I made my fortress able to withstand any standard siege or ambush without issue.
So imagine my anger and frustration when the enemy appeared inside my damn fort, completely circumventing my defenses.
An archaeologist I got from my first and only migrant wave dug up a marker. Suddenly some the animals I had to butcher to feed my dwarves since I couldn't devote time into agriculture with all the digging and item dumping I was doing. Since my butchery was right outside my front door all the necromorphs blocked off access into the fort (thus all the food, drink, and the dormatory) and they were able to immediately destroy all my workshops (which were just outside my front door).
I had to lock in whatever dwarves were inside and forced them to make a Temple so that I could get rid of the damned things. Meanwhile, all of my dwarves unfortunate enough to be outside were being slaughtered or chased around by the dead. Luckily, my food storage room was connected to the back rooms where I built the needed workshops for the Temple (Mason>Blocks>Stonecrafter>Candelabras) so the few dwarves in there wouldn't starve or dehydrate. I was also lucky that the necomorphs were willing to break down the front door leading into the meeting hall, but not the back door leading to the food storage so I had the time to do what was necessary.
Then I realized that I needed the marker as part of the banishment. By then, one of my two miners was dead and the second was crippled and stranded outside. I had to make a rockforge then a stone pick just to break out to the outside (since as I said, my workshops were built outside; including the archaeologist's study along with the marker).
Then the stupid happened. My dwarves, now free from the back rooms, tried to eat in the meeting hall and sleep in the dormitory.The necromorphs were in both rooms so I got to watch the few dwarves I had walk right into them. Then I got to watch as when one of the dwarves were about to banish the necromorphs he threw a tantrum in the process, destroying the temple.
By the end, I had four dwarves left. My poor militia commander that was being constantly strangled by a necromorph, my crippled miner, and two others. Then one of the those last two died before a dwarf could finally rebuild the temple and make the sacrifice.
Then I looked on in confusion as apparently; my dwarf sacrifice didn't die and turned back into a dwarf after transforming into a sacrifice, the necromorphs didn't die, and I had no way of recovering from there. So I abandoned the fort, then groaned in frustration when I realized I forgot to mark the map as a lair first.
So yeah, be careful with that archaeologist's study.