Well, no. AV wasn't in any way a proportional voting system. It was just a minor change in how you calculate who gets past the post first in the event of low voter turnout. He should have held out for a referendum on proper PR or no coalition. It was his one big chance to achieve what the Liberal Democrats and their predecessor parties had made a central pillar of their policies, even a defining characteristic of what it meant to be a Liberal in the UK, for decades. And he pissed it away for a sniff of a chance to play with the big boys.
A referendum on a confusing and ultimately ineffective change predictably fell flat. As it was intended to.
For the life of me, I can't see why the Lib Dems are siding against Scottish Independence. It would create exactly the kind of constitutional crisis that might give them another chance at electoral reform in England. Maybe they just don't want it enough any more.