If you really want to keep them all, I suppose it wouldn't hurt to try and keep them, but separate them into small groups. You say you have 9...so maybe 4 and 5 (or if you really want, you can take it further and keep them all in 3 groups of 3). You still run the risk of everything that came with the 'old' big flock (the one you have now) and the issues 2 or 3 new flocks would have, regarding the pecking order. Honestly, I myself would try everything in my power to keep them, if they were mine. But the choice is yours. It seems this topic isn't drawing so much attention. If Mr. Roo doesn't get back up on his feet within the next day or two, I suggest either renaming this thread or making a new one having to do with your rooster not being able to stand. Buff Orp boys are big fellas. And the condition of legs matters alot to chickens, as they cannot live without them. You have him isolated, yes?