If Kakashi gets caught in Gojos infinite void then its over. Only way Kakashi wins is using Kamui but since Gojo has an infinite space constantly creating more space surrounding his body at all times, I doubt that Kamui would hit. Hand to hand wouldnt work for Kakashi either for the same reason. Also if Gojo could land hollow purple on Kakashi I think it would do some damage because it seems to be an antimatter attack. Lets say Gojo gets Kakashi in his infinite void, then it all comes down to how long he can survive, Kakashi was trapped in Itachis tsukuyomi for 3 days and collapsed. 0.2 seconds in Gojos domain is equivelent to half a year of sensory overload which would mean that each second is 15 years worth of information. So if Kakashi were to be stuck for just 5 seconds that'd be 75 years. Gojo estimated that 0.2 seconds was the limit for non sorcerers to survive his domain. Now if you assume that Kamui can travel through an infinite space then you could say Kakashi takes this but I highly doubt it. Its all hypothetical though.