Joe Lieberman (I-CT) said on CBS's Face The Nation that he would rather no reform bill at all pass than see a bill pass that contains a public option. His threat to join a Republican filibuster against a bill with a public option makes it harder but nowhere near impossible for Harry Reid to get a public option if he really wants to. Possibly losing Lieberman (and presumably all the Senate Republicans) will deny Reid the 60 votes to overcome a filibuster, which would be needed to pass the bill through regular order. Lieberman's obstructionism is clearly a hindrance, but not an insurmountable barrier.
Harry Reid has never really needed 60 votes to pass health care reform with a public option, or the public option in a stand alone bill. Fifty senators plus the Vice President can do anything in the Senate if they really want to. While it would be more difficult and would step on a lot of precious Senate egos, Reid can get a public option using reconciliation, or even the “nuclear option.”
Reconciliation bills can't be filibustered and are still an option for Reid. Because of the Byrd rule passing all parts of reform using reconciliation might be problematic, but a stand alone bill for the public option shouldn't be a problem.
If Reid concludes that he doesn't want to use reconciliation, he can also use the “nuclear option.” The nuclear option would be a point of order ruling that would allow the Senate to eliminate the 60-vote threshold for cloture. Former Republican Senate Majority Leader Bill Frist threatened to use it just four years ago over the issue of judicial nominees. There is nothing Constitutional or even traditional about the 60-vote threshold for cloture. The rule about needing 60 votes to end a filibuster was adopted in 1975, and only recently so egregiously abused. In fact, the original rules of Senate did not allow for filibusters.
Passing a reform bill, or a stand-alone bill containing the public option, without 60 votes for cloture would be messy, but completely doable. While it is undeniable that Lieberman has just made Reid's job harder, neither Joe Lieberman, nor Blanche Lincoln, Mary Landrieu, and/or Ben Nelson can stop the public option--alone or together. As even Evan Bayh pointed out, if Harry Reid, Joe Biden, and 49 other Democratic senators are really determined to get a public option, there is nothing stopping them.