Is there a way to get the satisfy the artist with the fake ore and use the real one to upgrade a certain horn?

No matter what dialogue i choose he leaves. I did the quest before but I gave him the real one. Future Thanx To All.

Yes he leaves, but you can take the fake ilithium to the church anyway and they accept it as a sculpture.

And real one upgrades mace

If you talk to him with the real illithium and the faked in your backpack, he will always take the real one.