Yes I have had birds recover from an outbreak of Marek's. In fact one pullet recovered from two outbreaks. They always have the disease, but they can be perfectly healthy in between outbreaks of the neurological type. I have had birds that miraculously recovered after a few days and others that took months of supportive care. There are no hard and fast rules with Marek's as well as so many variations of symptoms all of which makes it so difficult to diagnose.