This is not a political post. :)
Pop quiz: What core D&D class has a class ability that may instantly kill him when it expires?
Answer: The barbarian.
Because of the way the Constitution rules work, a raging barbarian can die when his rage runs out if he’s 5th level or higher. +4 Con bonus from rage = 2 hp per level, which means 10 hp or more at level 5, which means that your hp drop by that amount when the rage ends, so it’s possible to drop to -10 or lower and just die. Which sucks. It’s even worse at level 20 when the barbarian’s Con increases is +8 (so you instantly die at rage’s end if your current hp are 4×20 = 70 or less).
It’s not just a barbarian problem … the bear’s endurance has the same issue, as does any Con-boosting item. Or Con-draining effect … it’s bad enough that poison can kill you by reducing you to 0 Con, if you’re injured it’s possible that the Con loss kills you in terms of hp damage.
It doesn’t have to work this way. To cite World of Warcraft (I know, shut up about WOW already), if your Stamina decreases (like from a buffing effect ending) and your health is greater than its current normal maximum, it drops to your current maximum. No “sudden Con loss hit point death syndrome.” Part of the problem is that everyone dies at -10 regardless of their max hp (something I addressed in The New Argonauts and Monte addressed in Arcana Unearthed, but mainly it’s the huge hp drop possible from a Con change.
Proposal: When your Con decreases, you do not lose hit points unless your current hit points are greater than your maximum hit points possible for your current Con, in which case your current hit points drop to your current maximum.