That said, navicular is some sort of crack or hole in the navicular bone that floats at the rear of the hoof attatched only by tendons (which pull on the bone every time the horse takes a step). And every time the horse puts weight on the affected hoof the bone is painfully compressed.
The horse's chances for comfort depend heavily on the extent of damage to the navicular bone. The best way to determine the actual present damage is x-rays. Your veterinarian should take x-rays of the navicular bone and rank the crack(s) for your farrier (there is an established ranking system, so your farrier should know exactly what the vet means by a certain rank) who can then determine the best course of action for your horse.