Larian Studios Forums Divinity 2 - Ego Draconis (English) Divinity 2 - Ego Draconis Divinity II: Flames of Vengeance - Add on announce

In the add-on you escape from the prison and get back to Aleroth, at least. No other details have been mentioned AFAIK about any previous or new areas you will have access to.

If you do not keep a save from the end of the game to use, you can start the add-on with a new character.