Cody was literally front and center on early posters, won the Royal Rumble (Which has led to a title match at Mania all but what, one time that I think they did it at EC?) and was presumed to be on the card when ticket sales opened.
Stop being ridiculous. Anybody buying a ticket was well within reason to believe the #1 babyface in the company would be on the card, just like your argument that Drew/Punk had to happen as a match because it was advertised.
They were not going to leave Cody off Wrestlemania. They would've had two whole months to slap together a bullshit match before leaving Cody off Wrestlemania. Hell, they would've done Solo vs. Cody before leaving Cody off the card.