More interesting, yes. But is it true? There are some people who would easily cave. And there are people who would rather die than break that kind of precept.
I think this is vanishingly rare. Most people will cave eventually.
But this is what dice rolls are for, right? 'It's DC 20 to persuade this guy, because of his oath never to drink'.
I'm not saying the players will do this. Just that if our definition of railroading leads us to believe a king unwilling to give up his kingdom is a railroad, then it is not a useful one.
We're starting with a presumption of good faith though right? Why are players asking for things that are completely unreasonable in the context. 'I try to tempt the old priest with some elven wine so he'll answer my questions' is pretty far away from 'I climb a rainbow and become an angel'