Ah, so you can turn in the crystal for access, out of order, but it shuts down the quest?
This doesn't affect me too much, as I am coordinating with my roommate the quest and the turn ins. We plan on doing it at least twice, as we have five characters between us to flag, and a sixth/seventh only in the unlikely event flags rot. I'm one combine shy of being in the final stages of the quest myself, so I appreciate the information.