With respect, what's happened to the lib dems is as irrelevant as the lib dems themselves.
So if you're right, and if I was a Tory, with JC looming and all his 'momentum', why would I call an election in the next couple of years? That's the ultimate turkey voting for christmas analogy. Might as well stick it out for the full 5 years. Again, and it's a point a lot seem to be missing, the Tories have the power and they get to call when the next election is.
Labour were given an unexpected early shot, and they've missed. They might not get another one for 5 years. If you can predict what's going to happen between now and 5 years time you're wasted on Bluemoon, and should be earning millions on the stock exchange. Perversely, odds are you'd be a Tory voter if that were the case.