The Jeremy Jones you are thinking of does not ride for Burton, he rides for Rossi.
UnInc was an experiment that did well but was too limited in its exposure thats why it is getting smaller, not because the Pros left.
DCP and Demarchi left Burton to start their own line, not because Burton canned them. Their contracts were up and they decided to leave. Watch out for their new line called "Yes We Can"
Forum is closing up shop in SoCal because thats what Burton had planned since they bought the line. They didn't want the factory, they just wanted the name. It's just business.
I don't think anyone will topple Burton, they haven't in 25 years and they won't in the next 25 years. It's a solid go-to brand for the weekend warriors and vacation people and will always remain that way.