It has to be a mutual decision between the fighter and the org. Kimbo wasn't just allowed to leave, I beleive Coker was pretty much obliged to not cater to Kimbos desires financially and his status quo per card and fights slated for.
Now Eddie is a different story and I think Coker will work harder to have him under the banner. I'm pretty sure he'll fight for Strikeforce.
Oh ic that makes sense