If all of FL-citizens are ‘undead’(you get killed- you resurrect), how does someone become "undeader" and a tomb-colonist?
How long do the tomb-colonists live? And why do they "die", if their flesh doesn’t rot(they would collapse in a couple of months, if it did)?
You don’t really resurrect so much as fail to die. A blow to the head will knock you out, but you’ll wake up a while later, wipe off the leaking brain tissue, and continue on your day. (Dallying with the boatman is probably a metaphysical activity that does not cause your physical body to vanish.)
This sort of damage adds up. Once you are too battered to walk properly, or to enter a drawing room without causing shrieks, you wrap yourself in bandages and go into exile among other beings who share your miseries.
A tomb-colonist has two ends:
the bruising continues,
bones weaken,
speech is lost in a marble hall of infinite corridors
a terrible end without an end
under the watch of the Permanent Surgeons
—or—
a hope of frost
and rebirth