I have talked about my dislike for the "save or die" mechanics; they disrupt the pattern of combat by introducing ways of overcoming ablative hit points and deciding the fate of characters on a single die roll. In this post I would like to present a number of ways to eliminate such "save or die" mechanics from D&D-esque games, enumerating their respective advantages and disadvantages, as well.
The Ladder of Conditions
The first route, the one 4E went, is introducing a sort of "ladder" of statuses. When a disadvantageous condition is imposed upon a character (normally as a result of a successful attack roll), the player makes saving throws at regular intervals, each failure further worsening their condition (e.g. slowed - immobilised - stunned).
Here's an example from Heroes of the Fallen Lands: the 4E Essentials adaptation of the classic Sleep spell. On a successful attack roll (Intelligence vs. Will) the target is slowed, which ends if the target makes a successful saving throw at the end his turn. If he fails, however, he becomes unconscious (which, again, is ended on a successful save).
Here's another example, this time from Monster Vault: the Medusa's petrifying gaze. First, the target is slowed (which ends if he makes a successful save at the end of his next turn). If the first save fails, the condition worsens to immobilised. If the second save fails as well, he becomes petrified (until a proper power of restoration is used, he is willingly kissed by the same medusa, or the medusa is killed and her blood is spilt on the victim's lips before a day passes).
I find this solution rather interesting because most OSR games tend to avoid using systemised conditions, possibly because it seems artificial and heavy on the bookkeeping end. However, I strongly believe that with well-defined and broadly applicable conditions and the right tools at the table (e.g. cards or tokens) they can be more than useful - a cornerstone of the system.
The ladder of conditions is based on providing clear mechanical bonuses and penalties, as well as signalling danger and creating tension ("I hope I make my next save, or we're royally screwed."). It has three adjustable variables - (1) the "size" of the ladder, (2) the duration of saving throw intervals, and (3) the severity of the conditions -, which makes it very customisable. Also, certain effects can be made of only a single step (like Hold Person in the 3.5 rules).
The downside of this system is that first these conditions need to be written; it is not against its spirit to use unique conditions for every situation, but then it becomes really hard to improvise and difficult to manage the effects.
Ablative Ability Scores
The second route, the one Justin Alexander went, is similar to how 3E handled poisons: through ability score damage. Each effect (poison, petrifaction, mind control, etc.) could be handled by damaging one of the six ability scores, applying the final condition upon the targeted ability reaching zero.
Here's an example from Rival Guide, a Pathfinder Campaign Setting book, for the Cockatrice's petrifying ability. When struck, the victim rolls a Fortitude save; if it fails, they take Dexterity damage. If their Dexterity is reduced to 0 because of this, become petrified, against which they may make a saving throw once per day.
This change would make ability scores more meaningful (now each point could make a difference) and multi-purposed, as each ability could be targeted by a variety of attacks. However, it would probably increase the required bookkeeping, as now there are six extra scores whose values are subject to change.
Severity of Effects Based on Hit Points
The third route, the one I previously proposed, is based on Courtney Campbell's social combat mechanics (from On the Non-player Character). The idea is to handle special attacks using non-lethal damage; when the amount of this reaches a certain threshold, a fitting effect is applied.
Here's an example from On the Non-player Character, handling "Anger" attacks ("You stinking fish-fuckers couldn't beat my grandmother at fisticuffs after a bottle of vodka"). A Charisma-based attack roll is made against a special social AC; non-lethal damage is dealt on a hit, which is immediately checked for two different thresholds. If the amount of non-lethal damage is more than the quarter of the opponent's current Hit Points, they become Insulted (they gain slight bonuses and focus the taunter); if it is more than half of it, they become Enraged (gaining moderate bonuses and fighting till death).
This would add only a slight amount of bookkeeping (i.e. the accumulation of non-lethal damage); however, perhaps a number of special defences need to be calculated that might replace saving throws. A simpler version might be using AC as is, but that would make Fighters incredibly powerful against all effects. Alternatively, the attack roll would be substituted by a saving throw.
Also note that these three approaches can easily be mixed within the scope of the game - or even in the same special attack, as well. For instance, a powerful venom might inflict the slowed condition on a failed saving throw, and also drain a point of Dexterity every time the victim moves; reaching zero Dexterity would obviously leave the victim unable to move.