From my understanding,Mirko is leaving to get some fights,get back to his best and then he is coming back. Dan White has actually agreed to this which is(shock horror)pretty cool of him. Here are some words form Mirko:

Some felt that Cro Cop’s departure was forced upon him, but he cleared it up by saying, “I had no problem in getting released from my UFC contract” and that “Mr. White acted very professional”. He admits that he never felt completely comfortable in the cage and that he hopes to, “return one day to fight in the cage.”

By the way, Cro Cop did respond to Cheick Kongo’s comment about needing steroids to fight:
“I have a message for Kongo. Listen, I thought that you are a sportsman, a professional like everyone else in this [COLOR=#330000 ! important][COLOR=#330000 ! important]sport[/COLOR][/COLOR]. You were lucky enough to fight against me during the deepest crisis of my career. You probably ate a lot of vegetables and potatoes to look like that? I’ll be back in the cage and I hope you will be in the opposite corner. Then we’ll see for how long you’ll be able to talk.”