If the tongue is hanging out you need to keep it moist. The chameleon won't be able to chew with it hanging out (or it will bite it off, of course)...so you will need to take it to a vet and have it amputated.
If you leave it and it bites it or chews it off, then its liable to get an infection. If it is chewed off the remaining part may slide back over the hyoid spike or it may flap around and annoy the chameleon.
Good luck!