What to beware of when dwarves are reliably sealed in a fortress?

Question

Once I walled up all the entrances and thought that I'm safe. I managed to make the fortress quite stable, i.e. resources are replenished by dwarves and they always stay happy.

But eventually I started to lose dwarves faster than they breed. This is a list of causes of deaths in a sealed fortress which are easy to forget about. Please help me amend it:

• Dwarf is scared to death by a ghost which I forgot to bury before sealing the fortress.

• After few years clothes fell apart, which caused surprisingly severe bad thoughts and led to tantrum spiral.

• Dwarf fell into strange mood while I did not have a certain type of workshop. He went insane.

• One of dwarves turned out to be a vampire and killed a number of dwarves before he was caught. Moreover, I had to kill the vampire as well, i.e. lost one dwarf more.

So, what can be added to this list? What else to beware of?

Answer 1

There are plenty of things to worry about in a sealed fort. These are the ones that I tend to forget about.

• Death by Player: The one that always gets me. Indifference, boredom, carelessness, whatever it is that will cause the player to do something stupid that gets dorfs killed, e.g. building and testing the spear-trap danger room before actually assigning all that metal armor I made for everyone.

• Death by Nature: As in Forgotten Beasts and cavern fauna, especially in Terrifying biomes. A FB carrying a syndrome to infect your entire fortress is a classic way to experience Fun™.

• Death by Mood: Dwarf going insane because you've shut yourself off from the world, and that oak-encrusted marble figurine he's trying to make just HAS to have an ingredient that can't be found without opening the doors. For me, I never seem to have any yarn thread when I need it.

Answer 2

• You can build memorial stones to bury dead dwarves without his remains/body.
• Make cloths, the most save way to do this (only way in a permanent sealed fortress) is to shear your larger creatures and make thread from that yarn. This can be woven into cloth and made into clothes. You could also breed creatures for there skin and produce leather, but your pasture needs to be very large to sustain this industry.
• Check the wiki for the type of moods, most of the time you need a craftsdwarf workshop for moody dwarves. That is if they lack any of the skills for other mood demands. With a sealed fortress and without excess to all the resources like clay or sand this can be impossible to fix without outside help. Just kill the dwarf if he goes insane.
• The vampire thing is more of a hidden thing and very hard to spot. Usually a vampire has a long list of families, kills and a good skillset. The skills can be shown easily by dwarf therapist, otherwise you need to check every migrant. Vampires can be a nice addition to your fortress if you do not seal it off. I usually recruit them into my army and set a burrow for them outside the fortress as a hunting field. Since the do not eat, drink or sleep they are perfect guards and often very strong too.

Simply sealing off your fortress is not a good way to go imho. As you found out it is easy to lose a dwarf and without migrants it takes a lot of year cycles to grow childs yourself. Why not seal yourself off with a raising bridge, just open it when migrants arrive. One problem though, the merchants will not bring there carts with them since they cannot find a path to your trade depot.