Me and my friends were debating a certain idea. Namely using demiplanes as a place to get resources from (such as fertile soil, organic matter, stone and so on. There was also the mention of metals though I'm not sure if demiplanes contain ores.) This raised the question of what happens to things that were part of the demiplane but got taken out before the demiplane expired. Do they cease to be or are they permanent now that they are in the prime material?
Regrettably, I couldn't find any RAW source addressing this directly. Thus my answer is a bit of educated guesswork. I honestly don't think that Paizo considered this, so obviously, consult your DM on this.
My best guess
Only creatures can get the extraplanar subtype, this loosely implies that objects (like earth, stone and non-creature plants) are not bound to their planes. This would mean the disappearance of the plane should have no impact on resources removed from the plane, even if it would affect creatures. And as far as I can tell there are no rules on what happens to creatures either.
Logically speaking though, I don't see any reason demons in the material plane would disappear if the abyss somehow collapsed. I would use the same logic here.
I'm not sure if demiplanes contain ores
Lesser Create Demiplane states the following:
The plane is generally flat and featureless, such as an earth, stone, water, or wood floor.
I doubt that a floor made from ores would be considered 'featureless', so you can't create ores with the spell. I also don't see any reference to metal in the spell. Even if some planes contain metal and/or ores, planes created with this spell do not.