Every server currently being used will be converted to WOW TBC Classic Gold TBC servers. Start new Vanilla versions of these servers. You can choose between activating your character on the TBC server or the Vanilla version. You'll have to pay to activate the same character on both.
Edit: Blizz's own piece on the subject. "On the day of patching, you'll be able to launch the Battle.net desktop app and choose the game you'd like to play--Burning Crusade Classic or WoW Classic. Both game types will display your existing characters with the old name/s of the realm. Once you've chosen a game to play, pick the character you want to play and confirm your selection. You can buy WOW Classic Burning Crusade Gold use an optional paid service to play the cloned character in the two game types if you decide to play as your character on both. All you have to do is log in as you normally would and play."
If you are looking for academic service, you should cheap college paper writing service to find out more. This site will help you find answers to your questions.