8th Gate needs to be considered a miracle technique in this war >.>. After having waited so long to see something we knew would one day happen, & then spend a chapter talking about it, Madara needs to get brutalized even if for a short while. To be honest I don't see Gai dying for some reason, the technique itself would kill him, but maybe Naruto gains the Kyuubi & boosts Gai's chakra limit, enough to keep him alive.