This entire post happened over a period of about three years.
I had about 100 dwarves by the time the Skeletal Dragon came. I locked my doors, and a year later after I had built up a military, I lost only 10 military dwarves killing it and had no fire incidents.
Then a Titan came. I lost about 10 dwarves. Now I have 80 dwarves, but my military was *decimated* because I accidentally had my archers "off duty", then when I finally noticed, the archers came and attacked with wooden ammo... Eventually only three crossbowmen were left, and I decide to demilitarize all but the one who killed the titan. I decide I can't spare any peasants from their hauling jobs, so I just let the one marksman practice his skills on the range inside.
Then a Skeletal Titan came. I figured hey, no big deal, I'll just close my doors in case it gets through my seven rows of sawblade traps, and maybe in a year I'll have some military trained up. I tell my dwarves to come inside, and then I go and deal with some stuff inside my fortress for just a few seconds. I noticed a couple cancellation messages due to the Titan, and I think to myself, "Dammit. Who the fuck is still outside..." So I hit [u ] and find the Titan, only to discover it run with the speed of a heavily laden african trade wagon to my gates, tiptoed past all my traps, AND is about two steps past the doors which I hadn't locked yet. I lost 25 dwarves after I activated the entire fortress (minus my 10 prized forge/smelter workers), and killed it eventually.
That's all that happened.
Except for the Skeletal Dragon that came about one month directly after that!! I figured the same as with the Titan, that I'd just lock my doors and wait until I could build a military or come up with a plan. I have around 55 dwarves now. This time around, I actually lock my doors so that the dragon can't get in. Except I mod my dragons for flying, aaannnd... I forgot about a channel I dug incorrectly on the surface, and I had holes in the roof of my underground farm, which was connected to my fortress... needless to say, the dragon descended into my farms and lit the nearby seafood pile on fire. This time, I had to activate everyone right off the bat, including my forge/smelter workers... I lost 25 more dwarves before I realized my prized marksmen (two of them, who had each killed one of the Titans before) were both holding adamantium bolts, but were OFF DUTY! About eight adamantium bolts and one burning fortress later, the Skeletal Dragon was dead, and I had only eight workable dwarves left (28 dwarves counting nobles and a crap-ton of children). One of the eight "workable dwarves" refuses to rest and is about to die, and two others are resting, so really only five dwarves can perform labor.
That happened thirty minutes ago, and I've been cleaning up the body parts since. And to add insult to injury, between the time I started and finished writing this, I came under siege by 34 goblins. They won't be any trouble though, since I'll open my front doors and they'll make a bee-line for my traps.
I'm going to try to recover this fortress without having to reclaim... wish me luck.