I don't know about that. I think there are many different definitions of success here. WP Engine would want to make sure that it's customers are well taken care of and have a solid web hosting experience. That would be success to them. I'm not sure how much they would care about outside users or developers (they might care a lot, but I don't know). But, the real question is -- would a fork benefit their customers?

If the answer is yes, then I expect to see a fork happen quickly. That may be the only way (or best way) for them to keep some degree of control over their system.