Sorry i am 5555cham i had to change my password because something was wrong with the login thing. My chameleons tongue looks all the way out. i have been misting it evey few minutes. it happened while i was feeding him last night.
I have never experienced this myself, but I do know you should see a vet asap. You might want to look at some 24 hour emergency pet hospitals. If your chameleon's tongue is damaged to where it can not heal, the vet will want to amputate.
Here is an article about a similar situation at adcham: tongue problem
What an incredible shame. I am sorry you lost him, and I am sorry for your vet's ignorance. Many people have been in similar situations and were able to successfully hand feed their cham. I wish he would have encouraged you to at least try.
From what I have read, it is not overly common, but it isn't unheard of. I am far from an expert, and haven't seen it yet. One of the big contributors to it is a lack of proper supplements and/or lighting. The cham develops deficiencies and it affects the tongue. It can also occur from damage when the cham shoots its tongue and wraps it around something, or bites it, etc. I am sorry your vet didn't see it as an option. Maybe there was more going on with the cham that led to his or her reasoning.
If your vet said that there was nothing that could be done, he was either not a good chameleon vet or he had other reasons for advising that the chameleon be put down, IMHO.
When a tongue won't go back in the proper place over the hyoid bone spike in the throat of a chameleon it can be amputated so that just enough of it is left to cover the hyoid bone. There isn't much choice if the muscle won't pull the tongue back in.
This means that the chameleon can't (of course) extend its tongue to catch an insect...so at first the chameleon will need to be hand fed. The ones that I have had experience with all learned to eat like other lizards that don't have the long tongue. Once they figured this out, they could live a normal life.
However, consideration needs to be given concerning why the tongue couldn't be retracted and hung out in the first place. It can happen once in a while by accident. (eg: the tongue got tangled on a branch so the tongue was injured.) It can also happen due to health issues....which (obviously) need to be corrected to bring the chameleon back into good health.