Spread the word. The Classic Server Data basically gets migrated over to the new server host, so anybody who wants to stay behind in Classic, won’t lose their progress. And may self delete, at their own disposal. There will be no character transfers between Classic and TBC and vice versa.
Meanwhile, the old Classic server progresses to TBC, so those that just want to play in Outlands, as soon as TBC releases, can. And those that want to start fresh, can do so, as well. And, those interested in playing both Classic and BC (raises hand) have those same options to progress their “Classic” characters or create a new a character.