Labyrinth Lord Wilds game. That said, stuff like poisons and diseases should still have consequences, so here are some ideas for eliminating the save or die mechanic but keeping the threat in play.
- Poison - Probably the easiest to fix. I treat poisons as a damage over time effect lasting a certain number of rounds. Low level poisons do little damage, say 1d4 per round for 3 rounds. A repeat application resets the duration counter full, so if Bill the cleric is bitten by a giant spider in round one, and again in round two, the poison doesn't stack potency, it just continues for another three rounds. A successful saving throw halves the damage going forward. Of course more potent poisons do more damage. Taking 3d6 per round for 6 rounds will kill the doughtiest fighter, especially he or she keeps getting bitten / stung, which renews duration.
- Death Magic - Yeah, you're dead. Seriously, if someone's shooting you with a wand of death, and you don't make your save, the consequences are clear.
- Disease - Diseases are long term problems for characters. When someone is first exposed to a disease, a failed saving throw means the victim is infected. I run most diseases as creeping attribute loss, and characters have to save regularly to slow the advance of the illness. For example a giant tick bite inflicts the character with a wasting disease. They have to make a save once every two days or randomly lose a point of strength, constitution, or dexterity. If an attribute drops below the minimum, the character is unconscious, and if it falls to zero, they die.
- Petrification - This isn't one that comes up a whole lot in my games (at least not yet). I've generally run it RAW when it's come up. Saving to fully resist the effect and having to make a system shock roll when / if your friends get you de-rocked seems fine. As an alternative, making a save versus petrification means the character is only partially turned to stone. You didn't need that arm did you?
- Massive Damage - Some systems require a system shock roll if a character suffers massive damage. I've never liked it and don't use it.