Aww, I hope you have more survival than you're currently expecting. My tank was gassed very badly a while back, too. And fish I thought for sure would expire turned out to be just fine. It just took them a while to come out of it. Really, it was a couple days for my plecos to stop flipping over onto their backs and for everyone to appear normal (and they remained normal and healthy and I ended up finding new homes for them because they wouldn't stop breeding!). I hope they're not brain dead - perhaps they just need more time to recover from the effects of the CO2. Wishing the best.