When I was growing up my aunt had a newfie, Christy. She was a great dog and encouraged my love in large hairy slobbery dogs. lol They weren't really dog people, though they cared for her and loved her in their own way.
Anywho, she was diagnosed with DCM and lived to be 10yrs old. She might have lived longer, but they chose to have her PTS when she started getting out of breath a lot. They were worried she was going to pass away and one of the kids would find her (like i said, not really dog people..) I'm not sure if they medicated her or not since it was around 12yrs ago.
All in all, I just wanted to let you know that some dogs diagnosed can live longer lives. Best of luck with Raven.
PS When Tenchi's seizures where closer together we were adding canned cat food since they have more taurine than dog foods. I think Lamb based dog foods have the least amount of it.