All dogs do adjust to this. Deafness will usually manifest itself as disobedience and a disinclination to bark. Blindness is a little harder to pick. I know many owners who think their old timer can see fairly well when in fact the vet has said the opposite. This shows how well dogs compensate for loss of vision.
Arthritis is another condition most old dogs suffer from.
Aspirin will relieve pain on bad days. Heart failure may present at first with a deep cough. Any older dog with a cough should see the vet immediately. There are many drugs that can be used to make the animal more comfortable an extend it's life. Many older dogs have decreased kidney function.