How did you cause the cave-in? Via lever or via miner / deconstruct? I always worry that any dwarf involved will get sucked into the damage zone by falling rock or earth tremors or something.
My spooky terrifying fort is going great. I'll admit that I've had to savescum a few times, but I have no shame in it from a "builder player" perspective. I'm playing for fun, and not to have the wildlife despawn and respawn right on top of the liason. That just leads to more "zombie surface with 7 dwarfs" which isn't what I'm planning to make.
I have found that making walls outside early on is key to a great Terrifying fort. If you can section off the map into halves, or even just build a really long wall, then you're safe on one side while the zombie grasshopper is on the other (Note: This may not hold true in the next version due to climbing). Again, I had to savescum a few times in the first months so that the wildlife wasn't lightning bird zombies. Just remember, a few tricks in the first year will make the next 99 years of the fort much more entertaining.
Well, I'm off to bridge to the cavern islands, and erect a blockade shelter over the river while it's frozen (I don't want to loose moody dwarves to the inevitable "gimme shells" requirement that will happen in the coming years).