Liberty Media CEO Greg Maffei wasn’t trying to put down Mel Karmazin.  ”Mel has done a great job” at the satellite broadcast company, Maffei told the Goldman Sachs Annual Communicopia Conference this morning. But he added that Sirius XM’s colorful chief also can be replaced once Liberty takes control — which could happen any day. “Graves are full of irreplaceable people,” Maffei says. “There are plenty of people who could do a great job…Without Mel the business will not fail.” The answer leaves open one of the key questions investors have about Sirius XM’s fate as Liberty prepares to take over. Liberty reported this week that it owns 49.5% of the stock, and is still buying. Karmazin said last week that he’s “open” to staying at Sirius XM. He added, though, that  “my instincts are that Liberty does not need me,” noting that “I have historically been expensive…That’s OK with Mel.” One likely key to any discussion is whether Liberty will hold on to Sirius XM, or plans to spin it off — possibly as part of a tax-saving process known as a Reverse Morris Trust. Maffei was coy on the matter. He says that Liberty will decide later about the Reverse Morris Trust but added that “our history has been eventually to spin off these businesses.” Before anything happens, Liberty will press for Sirius XM to return cash to investors, probably by repurchasing shares. Sirius is “an unbelievably strong business,” Maffei says.