According to a poster on tMB who goes by the name "LousianaHusker" Barney would of been retained if it weren't for Bo going nutty at North Star. Discuss
Warren certainly helped but Barney had been on Lee and Anderson prior to CW & really played a key role in landing them.
It's also my understanding that if Bo had not gone insane at North Star taking the entire staff down the drain with him that MR would have retained Barney for some position.