The creation rules note that an Adamantine Golem requires 4,000 pounds of adamantine, mithral, gold, platinum, and other metals worth a total of 100,000 gp.
Assuming the PCs actually manage to kill one (well, two, actually[1]... How much of that would be "useable," i.e. suitable, in terms of mass, to sell on?
Nothing?
50%?
Almost all of it?
I have no idea. It's not something that USUALLY comes up with golems, because those made of precious materials aren't that common.
I suspect the answer is probably intended to be "none" just like you generally don't expect to get money for the bodies or any creature... But I feel like my players are going to ask (in the long, long, looong time away this will happen), so it would be nice to have a prepared answer. If anyone knows of any lore or established guideline, I'd very much like to know.
Edit: Having thought more about it, and crunched the numbers, 200k is only 25k split eight ways, so it's not wildly out of line compared to NPC wealth, which, on thread-prompting to go look at, is more than than for a heroic NPC of the same CR. So bollocks to it, if they can kill the things and they can transport 4000lbs of it, they can have it!
[1]Chance is quite small, because they may well not have the appropirate vorpal weapon to hand and they don't have a cleric or wizard to cast Miracle or Wish. Don't feel too sorry for them, by the time they'd be doing this, they'll be level 17, eight of them and mid-tier mythic. Having to find a way to keep the things down while the fight and loot the last room of the dungeon should prove to be entertainingly different...!