What's the value of teeth to an adult dog?

Dogs get a lot of mental stimulation out of chewing as well. I'd take precautions (as it looks like you are!) to make sure he doesn't lose any more teeth than necessary. It's not the end of the world if he does, but I wouldn't just let him lose teeth left and right.

That said, I'm not sure you'd absolutely need to put him on a softer food. I know dogs with very few teeth that eat raw meat and bones just fine! Where there's a will, there's always a way.

Both of my Pomeranians are missing about 1/2 their teeth. I spoke with our University-Vet Department and they told me that in the wild, the dog would not survive, but being a domestic pet they will do just fine without any teeth at all. (I actually contacted them to see if they did dental implants on dogs)

I know it bothers you and it certainly bothers me, too, that my dogs are missing teeth, but he will be just fine. In the event of a toothless dog, there is wet foods that they do very well with.

ADD:

Even though my dogs are missing a lot of teeth, they still are able to eat hard, crunchy kibble. There is nothing that they can't eat....yet.

One tooth won't make much of a difference. He should be alright unless he loses the majority, which most likely won't happen. But if it does, aside from having difficulty eating, his tongue would also stick out of his mouth all the time. It's kind of cute in a way :)

Digestion begins in the mouth. Chewing breaks down food so that it can pass more easily through the digestive tract.

nope- I have seen many dogs that have no teeth left and do just fine