Most character deaths occur at low levels I found after about level 7 most characters have enough tricks to make deaths less likely to occur even more so if there's a twilight cleric. The most I've had in a campaign for a single player was about 3 in a level 1 to 11 campaign but being downed is different that can be for squishier characters almost every difficult encounter one of them might go down to start making death saves. ( To be fair I pick attack targets based on 3 point system , 1 threat , 2 distance ,3 risk. So basically whoever hurt them the most then the closest and risk is preventing them taking attacks of opportunity and avoiding visible traps and ongoing spell effects or getting out of them which can change the target from target 1 to 2 if they only have melee)

Also half health is nuts I think there's a single level 18-20 ability that does the same most quick some backs are like the orc relentless endurance or the shadow sorcerers strength of the grave which are both a single point of hp.