I got Pillar of Strength even though I chose to keep the malachite gems.
After the episode with the goblins, I went back to the enchanter and said that I kept the gems, to which he said something to the tune of "well aren't you a bastard".
I then had a dialog option to say "Can we upgrade anyway?" to which he said "Yes, but we're going to need some cash". After that, I got an option of telling Sassan that we were ready to upgrade the enchanter platform. I don't know how much gold she took.
