Jeanne,
Having lived with both dogs born deaf, and ones that have lost their hearing due to age I totally understand.
I think I will probably get upset when my hearing dogs get old enough to lose their sight or hearing. Not because I think less of them, but because it marks their aging in a definite way.
I'd start using signs for Oasis, as long as they're consistant it doesn't matter if they're "real" ones or not. Flashing lights and stomping work good for getting their attention, as long as you teach him what they mean.
Also exageratted facial expressions and body language help convey your feelings to him.
Cuddle him tight and enjoy his silver years. I really love those greybeards.