If this were a casino with a professional dealer, then provided there was no doubt about the "mucked" cards, then dealer's cards could be returned to him, UTG can make a decision, the hand could resume. A casino would have this covered in their T&Cs, I know this because I played recently in Brighton and was sensible enough to read their policies before playing.

Since the player who shoved is the dealer himself, it's a little more complicated. It's his mistake, he mucked his own hand. The manager would be acting fairly if he declared the dealer's hand dead, but asking UTG is probably acceptable, because it allows UTG to decide if the cards the dealer returned to himself we definitely the cards he was dealt. If UTG is under any doubt, the hand is dead. UTG was kind to the button here, but honest. Fair play to him.