As Ragnarok said, there’s no need to engage the goblins outside if they’re friendly on the way in as you can exit through the temple and Underdark, carefully sneak past them if you exit via the broken wall up top, or just fast travel (though personally I try to only do that when I know there’s a clear path to a portal).
I do agree with everyone who complains that all the goblins turn hostile immediately after killing Dror Ragzlin, and think that this should only happen if you leave and return or after a long rest or something like that, but it is still possible to sneak out using the rafters and thereby avoid most of the hostile goblins left inside after he and those immediately around him are dead.
It’s not easy, but I think with a party with stealth/invisibility options (plus use of spells like misty step or jump for added mobility) can indeed run this as a reasonably sneaky assassination mission which is great fun. Though I do agree that a few tweaks, and particularly a delay in remaining goblins turning hostile after Ragzlin is dead would make it even better.
"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"
