The collar is still there, on some level. Even after he'd seen both beloved mortals to their rest Gabriel couldn't bear to let go of the silver or the implication. A gift from the two he'd loved best.

"Close your eyes Sam. I've got you both. Just promise me you're going to fight, that you're not going to leave us."

He doesn't even have to wait for Sam's promise before Gabriel is slowly pouring more grace into him, using his power to heal and rebuild the damage that the trials had done. It was heartbreaking to see how the magic had savaged him, but it gave Gabriel enough focus to slowly help rebuild him.

It would take time, perhaps days, but he wouldn't stop until Sam was safe and whole.