Now that Spain has been "rescued" almost exactly 2 years after Greece, the situation is that the PP parliamentary group needs to start leaking parlamentarians, like PASOK did, until the government loses its supermajority and becomes vulnerable to a no-confidence motion. For PP parlamentarians to break party discipline seems unthinkable right now.

I think it's more likely that Spain's economy will tailspin to 30-35% official unemployment (60-70% youth unemployment!) and then social unrest prompts a suspension of civil liberties than that the PP will lose its parliamentary supermajority. The government has already legislated a criminalization of nonviolent civil disobedience.

But the PP base (and the parliamentary backbenchers) are right now in a state of perplexed shock both at the political/economic situation and at the government's performance (and performance art). So, who knows, there could be an internal revolt.

If you are not convinced, try it on someone who has not been entirely debauched by economics. — Piero Sraffa