I wouldn't bet a cent, not because his reasoning is wrong, but because the premise is wrong. The government doesn't control the main propaganda source: public education. That was transferred to
comunidades autónomas more than 30 years ago and nationalists have used it to brainwash people.
Did you know that it's impossible to have your children study in Spanish at public schools... in Spain? There were sentences from the Supreme Court and Tribunal Constitucional condemning this situation. Regional government ignored them and central governments did nothing for decades.
Other propaganda sources are not going to be controled either. There are a couple of associations, the ones whose leaders are now jailed, that play a central role and, unless illegalized (that I seriously doubt will happen) will still be receiving lots of money from the very same State that they're fighting. Why? Because cutting the financing would mean reforming laws that allow national parties to give money to their own fundations in other parts of Spain.
Public funded tv and radio would get new heads, but replacing the fanatics that produce the contents would need dismantling them, that most likely won't happen either.
Do you know why this situation seems so confusing? Because spanish governments have done nothing for a very long time. This has allowed nationalists to create the ilusion that they're really almost independent and they only need a little push to get there. Then our current prime minister is known for its "do nothing until there's no other option" style, that made the thugs think it's the moment to make their move.