Like I said in the other thread, fuling totems drop from fuling berserkers which are technically infinite in supply in a world until Yagluth is defeated, even though in practice the fuling attack event may come up rarely. They otherwise don't respawn.

Iron is fully renewable because oozers drop scrap metal, but I doubt anyone could be bothered farming oozers for iron when they could just start a new world and grab up all the iron there instead.

This game, like Terraria, is really not designed with long-term high-population persistent servers in mind. Since players can just go harvest nonrenewable resources from a new world, that is what you can expect them to do once things begin to dry up in their old world.