There's no way to reset the zone without effecting everything inside of the Underdark, so short of going back to your last save you are going to have to deal with it. It is quite possible to get Adalon's eggs while the city is hostile, provided you are prepared to battle your way through -- it's not as tough as it sounds with the right strategy and tactics. Obviously you would miss out on the quests and vendors within the city, though. Do you have an autosave that you could fall back on? Moving through party essential transition areas, like the Kuo Toa tunnels, the Elder Orb warren or the Illithid city should create an auto save. If you do, make sure you make an explicit (new) save before you continue.
My auto-save has the same issue, so I'm probably out of luck. I'm a bit bummed about missing out on the quests, but at least I should be able to watch some videos on YouTube to see what I missed. Thanks for your efforts.
Yeah, it's a bummer. But knowing what happens in the quests, I would be more bummed on missing the opportunity to visit the vendors in Ust Natha myself -- other than the architecture and the vendors, I always found Ust Natha rather underwhelming, personally.