RPGMemes

Yeah, I think there's a big difference between "I thought they were going to investigate the smith, but they're really suspicious of the wizard now and want to check her out first" and "they decided to forget about the whole civil war for the throne thing and open a BBQ joint for the local goblins"

Nowadays I'd probably just explicitly be like "Hey, so, when we started this game we agreed on a certain tone and direction. Specifically, it was going to be about a power struggle for the throne. Running a restaurant business in D&D sounds wild, but that is really a different kind of story and a different game. If you want to do that, let's talk about it. Otherwise, I'm asking you to stay more on theme."

Though I say that and my best game had plenty of "beach episodes". One time literally, after they saved some sahaugin from being subjugated by a siren.

Yes, of course. I'm not Dr. Bibber, one wrong move and you're dead. In fact I've only "killed" a character like this once. And even then I allowed the rest of the party to retrieve the corpse and resurrect them the next session. Usually my players are observant enough to notice the "Certain death this way" signs.

This is more of a problem with newer group constellations where people still need to proof how random and quirky they can be and where the player GM dynamic is not yet fully fleshed out.