How does a dedicated actor get out of a role?

like Christian Bale from The Machinist, Leonardo Dicaprio from Shutter Island, and Russle Crowe from A Beautiful Mind... like any roles an actor get to play there must be a lot of dedications. they might change themselves a lot just make the scene look more realistic. but how do you think they can get out of what they were trying so hard to be and go back to their real life?