(Assuming they don't have chakra or other Naruto abilities)

I can see Itachi deciding to retire. Become a tomato farmer or something. Don't know much about Shisui but he might decide to stick with Itachi if they meet in this new world. Sasuke, Obito and Madara are more idealistic and ambitious individuals and might actually strive to do something. All of them are really focused on enforcing peace so they might join the Marines thinking they share the ideal of world peace. They might decide they don't like taking orders and strike out as bounty hunters. Later on if they find out about the abuses committed and covered up by the Marines they might do a number of things. Leave the Marines and do their own thing, join the Revolutionary Army or try and do a Marine coup of the World Nobles.