My 86 year old father just went down the exact same road in November and ended up getting released to hospice care as they said he could not recover. Well, he comes off hospice care very soon as he has made a full recovery. Your father's doctors are doing everything my father's doctors did at the prestigious IHC Heart Clinic in SLC.
A heart transplant is very unlikely and a person your father's age, it just doesn't happen very often. They are doing everything they can to get his heart stronger, give it time.