I've been thinking about this a bit since I read it this morning, and I think the only reason they were able to get rid of STV is because it was only STV for Calgary and Edmonton. With a single party still able to sweep the rural ridings, they were given solid majority governments, which shouldn't be the case with "real" STV.
I have no idea how we'll get either half of the LPC/CPC to enact STV, when FPTP has them oscillating between consecutive usually majority governments, but I expect STV will be hard to get rid of once we've had a single election with it. Not much incentive for minority partners in a coalition government to accept moving back to FPTP, right?