What happens with presenting viewController after it presents a presented viewController. Does its instance live forward? Is it destroyed when it is obscured by presented viewController views? If it is destroyed, how do I tell the system not to destroy it, but keep it intact?
I'm designing a game in witch the game is obscured with a presented viewController when some button is clicked. When the player returns to the game, I want it to restore its state exactly as it was before presenting a viewController
The presenting view controller keeps it's instance, and control is returned to it after the presented view controller is dismissed. In fact, you should have the presenting view controller dismiss the presented controller if possible.
Since the instance of UIViewControllers stay intact when presenting (or pushing) another view controller, it is best practice to implement the didReceiveMemoryWarning method in your UIViewControllers to release any memory that you can (clear caches, etc). Any data you clear out you may want to re-populate in the viewWillAppear method.
Other info from the View Controller Programming Guide for iOS :
Support for presenting view controllers is built in to the UIViewController class and is available to all view controller objects. You can present any view controller from any other view controller, although UIKit might reroute the request to a different view controller. Presenting a view controller creates a relationship between the original view controller, known as the presenting view controller, and the new view controller to be displayed, known as the presented view controller. This relationship forms part of the view controller hierarchy and remains in place until the presented view controller is dismissed.