Literally anything is plausible...people do ALL KINDS of crazy, unexpected things. Sometimes those unexpected things signal the emergence of a long-latent personality trait (e.g. Bilbo going off with the dwarves) but sometimes it's just the circumstances. So I'm not sure that 'plausible' actually constrains the choices.
Look, I get it: some players will ignore the emerging story to do something optimal. A great example is when the party is split, and one group is listening to the other group get in trouble, and so they announce, "We go running back to join the others!"
That sends some people into conniptions of frothing anti-metagaming hysteria. And, sure, we all know that the real reason they are running off to join their friends is that the players, not the characters, know the other group is in trouble.
But...so what?
- Coincidental stuff happens. There are all kinds of reasons that the characters (if they were real) might suddenly have decided to return. Sure, you could ask the players to name one of those reasons, but why even bother? (Unless they have a really good/funny one they want to offer.). This specific coincidence happens in stories and movies all the time. And it can make those stories better.
- Wait...did they say they are running back? As in, not moving carefully and quietly? Oh, this is gonna be good....
In other words: I just don't worry
at all about what is going on in other players heads and why they are declaring certain actions. It's all plausible, the GM has infinite dragons, and I just want everybody to have a good time.
edit: wow so many typos....