So just for the hell of seeing what would happen, I made a small (2x2 embark) fort with very simple accomodations. No personal beds, just a barracks, and the tables and chairs for the dining room are no-quality.
That's almost the entirety of what I've done with it. I dug a little lower to get some stone for the smelters (I added a custom reaction for free wood, in case I need it for something), but other than that I didn't touch anything. The stairs on the surface are walled off.
Aside from farming and making the occasional bag or barrel of booze or something,t here's nothin to do, so they spend all thier time hanging out in the dining room talking to each other.
Everyone's ecstatic.
Suddenly...
OHSHITGOBLINS
Since I have the entrance to my fort completely walled off, they can't do anything. They just kinda mill around for a few months. Originally I had just intended to wait for them to leave, but evidently they weren't going to do that. Then I got curious...
All my dwarves had no less than a dozen friends. Some were married, and everyone was ecstatic. What would happen if some of them died?
I drafted all but the first seven and sent them out to fight the goblins.
(KEKEKE ZERG RUSH)
Thirty-nine unarmed, untrained, unarmored dwarves pretty much steamrolled the goblins, including another ambush squad that appeared after they engaged the first. Three dwarves died.
Everyone's moods afterward.
They're all still ecstatic The living ones, anyway. Being drafted, seeing thier friends murdered, and several of them being injured wasn't enough to dampen thier moods in the slightest.
Apparently losing a friend works similarly to how losing a masterpiece does- i.e. if a dwarf only has one friend and his friend dies, he'll take a major hit to his happiness, but if he has a dozen friends and one dies, the negative though from it will be relatively minor.