Would non-magical equipment from a dead adventurer be usable after X years in a dungeon?

Ok, so there’s this adventurer who died in the dungeon some years ago. Nobody took their equipment (maybe they died of poison, whatever). The PCs encounter the body years after. Naturally, they want to use the equipment.

Let’s say the dungeon is moldy and wet.

Would boiled leather (i.e. leather armor) still be of any use? What about normal leather (backpack, etc)? Steel weapons? Wooden weapons?

Would it be different if the dungeon was dry and vented?

I’m running a survival-themed campaign, so these kind of things worry me these days.

Any help would be appreciated. Thanks!