Yes, from the Official FAQ (can see it here http://wiki.dominionstrategy.com/index.php/Prince)
"If you don't discard the Action then you stop playing it with Prince; Prince at that point is just set aside doing nothing for the rest of the game. That won't normally happen but will happen for example if the Action is a Feast or Mining Village and you trashed it, or if it's a Duration card and so it stayed in play, or if it's a Madman and was returned to its pile, or if it's an Island and was set aside, or if it's a card you put back on your deck with Scheme."
"If you don't discard the Action then you stop playing it with Prince; Prince at that point is just set aside doing nothing for the rest of the game. That won't normally happen but will happen for example if the Action is a Feast or Mining Village and you trashed it, or if it's a Duration card and so it stayed in play, or if it's a Madman and was returned to its pile, or if it's an Island and was set aside, or if it's a card you put back on your deck with Scheme."