What difficult news to hear... Personally, I think you should find another galah breeder. If you were to get another bird from Bisou's breeder, would it be out of the same parents? Even if it were, that doesn't mean it would have the same disorder. I assume this pair has produced many chicks, and the rest of them have been healthy, or he wouldn't have kept them together. Is he the breeder? If he isn't, can he find out this information for you? These are questions I'd ask before making a knee-jerk decision. As for a severe macaw, they tend to be one person birds with very "nippy" reputations. Macaws in general are very "beaky" compared to cockatoos, and severe's are even more so. If you aren't comfortable with this, don't try to take one on. If you first chose a galah, I don't think a severe will be a suitable match for the same criteria.