It'll never happen. But Punk retains against the rock before the actual rumble match. He goes into ultra smug mode and sits at ringside on commentary throughout the royal rumble match and runs down every entrant. He gloats and boasts that no matter who wins, they will never be able to reach his level, he's the champ, he's beaten all comers, even the rock, and will carry on holding the belt and break sammartinos record.
He jokes, he snipes and he sits grinning with his feet up on the announce table watching in glee. He even waves off cena, if he wins, meh. The rock dropped cena and punk dropped the rock. There will be no more mumbling about the attitude era, or waiting around for John cena to "take back his brace ring", its his time, it's the punk era and he is the best in the world and the greatest of all time.
number 30 enters. And we hear the glass... Fill in the rest. Although punk would retain at mania.