Thanks for the advices. Though I know (and use) them, they are still workarounds which any starting user won't be aware until it's too late. For some reason, mob corpses are containers when you open them with a knife, and players are not. My point here is that it's counter intuitive, inconvenient, and the corpse mechanic should be a standard for all entities (players and mobs) of the vanilla game w/o mods.
If inventory is reclaimable, the process should be reliable. If not, the condition should be clearly delivered in some in-game guide to warn players. Perfect option is a config parameter (which is partially there, but with only two options: keep or drop the inventory, not destroy it). Main point is that it should be a part of the base game, not mod.
My current vanilla experience is "you should be able to reclaim your spilled inventory, but it's a gamble, as it can despawn at some time I can't predict, if it's in a distant chunk". There's no ingame guide that explains it