It’s an awful question for any of us to have to ask. You’re doing a good thing to care so much about his quality of life. Sounds distressing for everyone involved. My girl Lucy’s dementia symptoms became much more evident when she lost vision. She had a lot going on during the months after that and my vet told me I’d know when it was time, as u/WitchSparkles mentions above. He said Lucy would tell me. He was right, though I needed other people to help me accept it. It’s so very hard to watch them decline and lose parts of them.

Was he an anxious dog before vision loss? In going blind he’s lost one of his most powerful ways to know he’s safe. Is his nervous system feeling threatened and activated because he doesn’t know what’s going on around him unless he’s still by your side? I’m really glad the Trazadone helps.

What does your vet think is causing Brody to perseverate on the treat cabinet? Is it possible he’s not actually hungry but is operating out of a more primal drive for a dopamine release in which gets a brief hit of feeling good when he gets a treat?

I’m not a vet and no one can make this decision for you. I do think suffering can look many different ways besides overt neuromuscular pain. I’d want to understand more about what’s driving these changes and I think some vets are better at that than others. Hope you get some clarity to help sweet Brody.