Two ways to avoid the Githyanki fight while keeping in spirit with finishing the quest:
* Under the right circumstances, if you're a Githyanki or disguised as one you only need to pass one Deception check to get them all to leave. But note you don't find the creche's location if you don't first...
* You can sneak up on the gith and pickpocket one of them for the creche's location. Depending on your criteria for finishing the quest, you could just do that and leave.
Both are a little luck dependent, although I imagine they'd be quicker than doing the fight unless you were really unlucky with ability checks.