So the best part, obviously was to watch the undead rising undead.
To test it I have came to a random dwarf fortress and raised 5 of these type.
In the entrance level there soon have been only walking dead. Then I flew down by stair case and spent some time in two main levels below surface. Almost everywhere I went I have seen dead bodies, occasional undead and sleeping survivors, but overall the fort population was slaughtered (the next day, though, the population restored to a degree, but dead ones came after them again).
I was staying outside for some time and seen a bunch of undead lurking around
Thee thing, however was that they didn't leave fortress region, and world-wide apocalypse didn't really happen.
I had approached some of them in wilderness.
These guys were not mine companions (they were not listed as such), and some of them attacked my character (apparently because [MEGABEAST] token in it).
This image shows how resistant these undead to death. While burning in the dragonfire, this particular corpse had been re-animated every instance by some other corpse.
And the most interesting part was when they all had came to a fort entrance. I then came from traveling mode to see them and was quite surprised to see that they are in a formation, probably even around their undead leader.
They immediately engaged dwarfs in the entrance and after some time they went after me and I decided to just burn them for good.
You may notice the blue text appearing that indicates some of the undead being risen.
After that I have decided to check history and I had indeed found many interesting instances, like this one:
So this all, in my opinion, justifies being a deity character. You trigger some stuff and you can see how it develops.