I think it would be satisfatory to not even bother with an excuse. PCs just get the privelege of being KO'd instead of killed so they can be pseudo-resurrected. PCs already have the privilege of "death saves". This would just be an extension of that because it's a video game and permadeath would just lead to save-scumming with most players.
You can create a narrative reason for the death privilege (eg your idea of deathproof tadpoles). But I think having an excuse is optional. Whether there's a narrative reason or not, they're not going to fool anyone into thinking it's not just a convenient video game mechanic.
Either way if we can avoid explicitly saying that player characters die, it would be better. I mean, setting aside the tadpole problem, I feel like literally dying several times a day would have to be quite traumatic.
