As far as I can tell, Meteor Heads are the only enemies that work this way, but if there are more, then they should also follow this rule. If a drop is obtainable from a creature before you enter Hardmode, it should still be available once you've passed that threshold. For many creatures, the drop chance decreases as more items enter the pool, but they never disappear entirely. I don't mind having a list of renewable and non-renewable items, but an item should not be renewable up until a point. It's difficult enough making large builds out of rare blocks like meteorite as it is, it gets far more frustrating being halfway though a build and finding your all out of the block.
And, I know it's an option to just start a new world, but as someone who likes for all of there character/world combos to be self contained, it seems like a very minor change to just have Meteor Heads stay consistent.
And, I know it's an option to just start a new world, but as someone who likes for all of there character/world combos to be self contained, it seems like a very minor change to just have Meteor Heads stay consistent.