Do horses ever actually fully recover from possums disease?

It seems you might be referring to Equine Encephalomyelitis, commonly known as "Sleeping Sickness". This is a viral disease that affects horses, not possums.

There is no cure for Equine Encephalomyelitis. While some horses may survive the initial infection, they often experience long-term neurological damage, and many die.

Possums, on the other hand, do not contract Equine Encephalomyelitis.

It's important to distinguish between diseases and the animals they affect. If you have concerns about your horse's health, it's crucial to consult a veterinarian.