As a political party the Liberal Democrats are finished. More's the pity as I believe that three party politics is far better than two.
But as a leader of a political party, when you stare sternly in to the camera lens and state loudly and clearly that under no circumstances will X, Y and Z happen and then subsequently capitulate and allow X, Y and Z to happen and then try to justify your massive u-turn by arguing that you never actually believed that you'd be in a position to implement your policies and now that you are, you can't because the political party you've got into bed with won't allow you to have your way..... you and the party you represent are finished.
If Clegg had any decency, he could force a vote in Parliament to declare 'no confidence' in the present Government and withdraw his party's support from the Conservatives. If successful, the current coalition would have no choice but to call a general election.
This won't happen of course. Clegg knows that he's the leader of a political party that has little or no public support. So instead, he'll continue to publicly support the coalition even though he must know that both he and his party are dead in the water. Only arrogance and the will to cling on to power will prevent him from doing the decent thing.