If you really believe he is in danger - call 911 and report it. And if he calls, you can tell him that you will do that. That sounds like a reasonable choice, to me.
Can you call the 911 folks to have him checked on, then leave your house for a while? Perhaps get a hotel and just sit in the quiet and soak up the peace?
Just for a day.
You may not be able to force him to see the value of your help (if I were him, I would be terrified of owing anyone anything!), but you might consider writing up an invoice that shows the monetary value of all you have provided, minus what he has given you with a balance of ZERO.
Then let him know you are stepping away and give him (or the family) the list of resource numbers they can call.
You don't have to be his savior. His life will be more uncomfortable... at first. But eventually, another caregiver may learn to understand his speech, too.... after all, if you could do it, can't someone else also?
((((upandopwnjj))))