They wouldn't be able to air episodes with Milestone characters (Icon and Rocket only, so far) in them in that case. But I suspect either DC has the Milestones completely bought, or at least has a pretty long lease, since they're focusing much more on their properties now than they used to.
(Also, one thing that many people, including those who sold their characters to DC, never realize, is that one of their motives is to eliminate the competition
. Sure, they might have plans for them, but if they fail, they can just shut them down and still "win" from their POV. This practice is OLD (DC has also absorbed other companies before, like Fawcett Comics and Quality Comics) and hardly limited to them (Marvel also ate up The Ultraverse
). Comics is a dog-eat-dog world sometimes.)