I'm regaining ground against the undead occupation of Saltcanyon. I managed to get all the corpses out of the river (well, all the living corpses anyway) by draining it into the caverns. Which was a pain, because it's actually 2 rivers. Water flows on from the north and west, but only flows off in the east.
The dwarves are slowly but surely building a ceiling over the section of the fortress within the canyon itself. I thought I had gotten them enough sunlight to avoid cave adaptation, but the trail of green coating my nice kimberlite blue entry road says otherwise.
I've been under siege by precisely 3 necromancer experiment invaders for... maybe a year? I decided it's not even worth it to try and kill them. The zombies on the surface outnumber them by a lot, never leave, and can't have their pathing manipulated, which makes them the bigger concern.
I'm keeping the magma option as a last resort. I don't have enough dwarves to pump magma that far manually and machine power is risky. If lava flows into the river, the waterwheels will lose power. I'm trying to figure out if it's feasible to set up a minecart shotgun that fires out onto the surface without ever actually letting the dwarves access the surface to build anything.
I managed to get a Forgotten Beast (a shelled humanoid made of coral) to the surface, where it successfully crushed a single intelligent undead before the swarm of failed Experiments of Curo chipped it to pieces. Well, progress is progress I suppose.
I broke out the walled-in weretortoise and sent her out through the caverns to demand tribute from various civilizations. She didn't succeed, nor did I expect her to. All I cared about was making contact. If they send caravans, that means caravan guards, who may be able to at least kill the various undead arms and heads crawling around. I even had her demand tribute from the goblin capital a full 16 days' travel away. Because at this point, goblin sieges would honestly be an improvement.
I was going to send her out to explore some abandoned towers in hopes of finding a necromancy book, but she decided she needed to pick up equipment, wandered a bit too close to an enormous zombie blob and got herself killed. It's a shame I can't just have the dwarves read that native gold slab I... acquired from a visiting olm man necromancer a few years back.