There have been some rumours for quite some time about Carlos Sastre negotiating with other teams. The rumour mill have been feeding on the fact that Sastre still hasn't renewed his contract with the team.
But according to sporza.be today, Riis seems to confirm that Sastre is leaving Team CSC-SB. With quotes like "Sastre isn't the future for team..." and the future belongs to Cancellara, the Schleck brothers and C.A. Sørensen. Riis also mention that paying these rising stars makes it difficult for the team to also pay (more) for Sastre.
Of course Riis could practice brinkmanship negotiating with Sastre, but it does seems more likely that Riis grew tired of Sastre's waiting game tactics and is releasing him from the team when Sastre's contract expires.