According to what I've read, the type of tumor he has is very severe. The fact they haven't mentioned surgery as an option tells me it's inoperable. An inoperable brain tumor in a 76 year old man pretty much means one foot in the grave and the other on a banana peel. I hope however long he has left is comfortable and with a minimum of pain and discomfort.
He's not dead and no, we shouldn't discuss him in the past tense as though he were. The type of tumor I've read that he has, gives him anywhere from less than a year to live to 5 years to live. Even at his age, that's a grim prognosis.