Not good, but they have survived such a thing.
Keep an eye on its mouth for fillaments. If it starts to come appart and turns it's stomack contents outwards it will die.
But if it starts to take them back inside he will survive, a split will usualy follow this trama.
Do a water change NOW to make sure that your water is clean and fresh and keep an eye on him, usually this will go into hiding to heal so watch for any deterioration of his mouth and good luck to you.