@Inezpri
You want slider revolution for your theme which you want to put sell on themeforest right ? Ohk then i guide you how you can use it without any trouble from its Author.
If you purchase revolution slider’s extended version then must note that you use those slider licence for your ONE THEME only. In future if you like to upload new theme on themeforest with slider revolution then you must Buy Second extended licence for that.
Thats the policy about existing envato item which you want for your item which you want to sell on envato marketplace.
if you still doubt then contact revolution slider’s author. its team must guide you perfectly or contact envato support team.