First night we killed Twemps. Second try. This despite the fact that 50% of the raid had never fought them before. Still, a lot of guildies were saying we didn't need TH, that it was a fluke. Second night was teaching them Cthun. Most of them got it, some people didn't, but with two guilds worth of people to draw upon we can replace people if necessary, or not invite them in the future. Third night we killed Cthun. A few bad starts, around midnight we got our first decent attempt - down to about 80%. Everyone agreed to use their good buffs and commit to another two hours of raiding, and we dropped him on the final attempt of the night.
There still might be opposition to a merger, but it's hard to argue with results.