It's always best to go with the tried and true food poisoning. Up all night, diarrhea, vomiting, lost 15 lbs, had to drink a full gallon of water before pre-judging, your guru didn't think you'd make it onstage, etc.
IF this happens - and only crazy conspiracy theorists believe Jay will back out -
The fans will react:
"You'll get em next year Jay!"
"Good effort!"
"He was still heroic enough to attend the after-party, very brave and shows he cares about the fans".
"You're still #1 in my book, Jay!"
"Phil is LUCKY that Jay ate bad fish."
And of course, Jay will paint it as a victory with "In my eyes, I did win the contest - the contest to reach my best ever shape. I missed this show with food poisoning from some bad food that was a result of some switched tupperware, but I proved all the haters wrong.
They said I couldn't come back AND I DID... I may not have been onstage, but look at these pics, I DID IT YOU HATERS! Shawn Ray, how you like dem apples? I did it, and you said I couldn't!" Then he'll promise to take the title next year, and anyone with a sub-75 IQ will believe it.
He is smart enough to frame it as a win, and of course, his fans will agree. Shawn will be shaking his head with "how the F did I get owned? I said he'd miss the show, and he did'. Jay, of course, will paint it as his real mission was to get in competition shape, and he did that, so he wins.