TM54 made a pretty good point on his blog about the Cubs and what their options are re:Dempster. If Dempster is only willing to go to the Dodgers, and the Dodgers won't give up Lee for him, then the cubs should go ahead and send Garza - who the dodgers will apparently deal Lee for - to LA and then re-approach Dempster. Tell him his options are to go to ATL or stay with the team the rest of the year.
Garza's left the team to be there for the birth of his child and may not start again before the deadline. That inactivity combined with leaving his last start early with a cramp makes him unlikely to be dealt unless the tide changes.
Really, Rosenthal has the leverage backward in his article. The Cubs do not have a ready made replacement for Dempster's innings, and they have plenty of payroll flexibility. They could very easily make him the qualifying offer to help salvage value in the form of his innings in 2013, as well as try this again at next year's deadline. Furthermore, the qualifying offer pretty much guarantees that he would be back with the team. No one is going to give up their first round pick(and slot money) for the right to pay 36 year old Dempster 3/36 or whatever FA deal he's looking for. That means that Ryan should think very carefully about using his veto power in a trade, since if he gets dealt, his new team can't make a qualifying offer. He can gamble that the Cubs eventually come to an agreement with the Dodgers, but if they can't get proper value for him, he's risking tens of millions of dollars of his last FA deal by saying no to the Braves(or other suitors).