Your argument is well stated. PR by itself would not have prevented the cuts, but other systems might have (e.g. potential recall of candidates, but citizen-initiated referenda are another possibility).
But that wasn't the point of my post. I was just pointing out how superficial and baseless the "No. The end" statement was.
Here's the thing: Anyone who categorically states that they *know* defeating AV at this referendum will have good longer term consequences is peddling exactly the same sort of unproven, speculative BS as the folks who *know* it is a stepping stone to a more representative system. The only certainty in this choice between two crappy alternatives is that the consequences of a No are about as difficult to predict as the consequences of a Yes. Maybe a No brings down the government, maybe it leads to renewed efforts for more proportional voting reform. But maybe the Lib Dems, seeing a thrashing at the polls should the government collapse, figure that the only option is to cling on and hope things get better. And maybe the pro-FPTP spin machine (e.g. Tories, most of Labour, all of big business including most media) convinces the overwhelming majority of the public that the people have voted for FPTP. Same thing goes for possible outcomes of a Yes.
It's a shitload more complicated than "No? The end."