Doomed? No. Collapse is not inevitable. However I think it's likely and would put a timeframe of less than eighteen months on it. If in eighteen months the Liberal Democrats are still polling around 10% in opinion polls, I think they'll have to leave. The longer they stay the longer it will take to repair the damage. Being in this coalition has hurt them hugely. They've destroyed two decades of careful building in two years. Indeed, it might well be more than that. As a political force in the House of Commons it looks like they're finished for a while after the next election. How long it takes to rebuild will depend on how forgiving the British people are and that'll depend on how long they stay. What do they even have to show for it? A laughably failed referendum on AV that even the strongest proponents of electoral reform (such as myself), found hard to justify, and House of Lords reform that I also hope fails miserably.