As a bit of an update to this:
I installed relentless assault, embarked with a river and magma pipe. I rebuilt my previous fortress, but decided to flood the area outside my walls with magma so my 3 tile wide road was the only way off the map. I then frantically filled the road with stone-fall traps which managed to keep invaders at bay. But then, the slime came. They came without any warning and walked right over my traps. They made their way into the fortress, breaking things as they went. They murdered all but 4 of my dwarfs and eventually died, sending miasma clouds all throughout my fort. Soon two dwarfs died from their wounds, and a third went berserk. After a bit of a chase he murdered my last remaining dwarf and my settlement crumbled into dust.
Dwarfs aren't phased by mass genocide though, so a new party of several axedwarfs reclaimed the fortress. As they arrived on sight they found everything a mess, but things seemed quiet and no harmful creatures were on the map. So they put their axes down and began picking up tossed barrels of dwarven rum, and claiming the clothing of their dead kin. Not two minutes later "AN AMBUSH! CURSE THEM!", oh crap. I looked to the entrance to my fortress but didnt see anything, but my dwarfs started dropping dead, one-by-one. I drafted everyone into my military and they went running for their axes. But it was too late. Four of my dwarfs were down already, but the three others managed to grab their axes. When I finally found where all the destruction was coming from, two more axedwarfs had died. "YOU!" I shouted as I hit the "K" key and found my berserk dwarf from the previous fortress covered in blood, and bulging with superdwarfinly tough strength from chatting at the meeting zone and flexing his muscles to the she-dwarfs. He was already seriously wounded, but my last remaining axedwarf managed to kill him with only suffering four yellow wounds. He then fell into a deep depression, and dragged himself over to the magma pits and promptly through himself in.