That sucks, first and foremost. Not laying blame, just a crapper of situation. I'd be curious as to how qualified the PetSmart vet is to make a determination about the well-being of a corn snake, as the ones around where I live are strictly small animal (ie: dogs, cats) vets and NOT "exotics" (ie: rabbits, snakes, etc.). You could continue with what you're doing and make sure he's as comfortable as possible and just keep an eye on him. Depending where the "kink" is, I'd be concerned with him being able to pass urate/stools, not to mention if he has internal injuries or not.

I don't know the entire story but from what you said, it doesn't sound like the store is too concerned about him; he dies, they just get another one to replace him and write it off as a loss. You could ask if they'd let you take him in but then you're assuming 100% of the cost for his medical care and upkeep. Crappy situation, whichever way you consider it. I'd be concerned about internal injuries and whether the "kink" is a spinal injury or life-threatening. I dunno...good luck to you and he both, whatever comes of it!