No, like Bowser, they'll come back in a later Mario game. Or in the Koopalings' case, in a game 10 years from now.
Uh, Mario wasn't gawking in SMB3 or SMW. He was just standing there with the same face as always. He can be dodging cannonballs and he still looks smug. It's like he knows we're Power Players and we'll safely get him through each level.