It is a very simple model.
Each character gets 1000 hit points.
Damage levels calibrated on a lower-ish side, OSR-like (i.e. not 50+hp per attack as it often gets in Pathfinder / 5ed), so 1000 hit points should lasts for a rather long while.
There is absolutely no healing of the lost hit points whatsoever by any means.(*)
One might consider themselves cursed, if it helps to frame it. Pain Saints will probably avoid such accursed, as they are nothings to exhalt.
Extreme hazards (falling from a significant height, walking through lava) half the current hitpoints to the nearest even number (1000 → 500 → 250 and so on).
Once hit point counter hits zero, the character is either dead and dissipated or is irrevocably a part of Gheste, often literally becoming one with walls and structures.
Disadvantage of such method is that numbers will be unavoidably mishandled by players. Counting down with no ways to stop it except to stop playing might also be depressing.
Advantage is that there is no need for dedicated healing class or long camping rests, which rather fits Gheste wandering nature.
(*) One can fully or partially reset their hit points by rewinding (or sacrificing, if it makes it more meaningful) their own being, specifically acquired skills and levels back to the previous stages.
(**) It can be used in Rooms, with some adjustments: as drifters, at least before a certain point, can leave Rooms to go back to stable world and use its logic to heal, the allotted amount of hitpoints should be smaller, about 200 per expedition per a character. Each hit points deduction will have to be noted separately for a little while, as they crystallize in jewels and the bigger the wound the bigger would be the jewel – as, unlike in regular Rooms, players under this model won't be able to 'gamble/bank' injuries to create better gems this is why some tracking is needed for each separate HP deduction before the crystallization fully takes place.