Look at the Philippines, South Korea, Singapore, etc. Authoritarianism doesn't have to increase indefinitely. Even in China the (very slow) trend has been to loosen up over time.
Assad's regime is doomed - agreed. Eventually. The time when massacring thousands of people in your country as a successful policy to retain power is over. But he, personally, may die in his sleep.
NK isn't Syria. They have a chance to liberalize via the Chinese model. And they have a lot of incentives to move toward integration with the South. Trouble is, their ideology wrt the South has been so poisonous it may take a generation for their policies to change.
FWIW.
Cheers,
Scott.