As long as the large RJ's are permitted flying in section 1, they can be flown anywhere, at any rates, even on the Delta cert. Even when DCI falls apart, you will still have to spend negotiating capital to bring the RJ rates up to mainline standards.

Also, since Endeavor is ALPA, single carrier status does not apply with the NMB, so there can be no staple, unless 51%+ of the Delta pilots vote for it. Not going to happen in 100 billion years.