That would be awesome, although hard to implement.
A slight twist on that would be the classic, "Yes, Minister," variant ("Yes, Gandalf"). The party is always given orders and it is their job to skillfully ensure that the orders are not carried out.
Gandalf: Do you think it is a good idea to destroy the ring?
Party: Well, Gandalf, in practical terms we have the usual six options:
One: do nothing.
Two: issue a statement deploring the ring.
Three: lodge an official protest with Sauron.
Four: cut off aid to the orcs.
Five: break off diplomatic relations with the Nazgul.
And six: destroy the ring.
Gandalf: Which should be it?
Party: Well:
If we do nothing, that means we implicitly agree with Sauron.
If we issue a statement, we'll just look foolish.
If we lodge a protest, it'll be ignored by Sauron.
We can't cut off aid, because we don't give the orcs any.
If we break off diplomatic relations, then we can't negotiate with the Nazgul.
And if we try to destroy the ring, it might just look as though we were over-reacting.
Well, some people say they play all gritty and realistic.
Let's put that to the test!
On the other hand, I don’t like the idea of events that happen no matter what the PCs do.
Games where we played Knights of the Round Table are games where we weren't the Big Heroes. I've also had games where the NPCs were more important, like being the bodyguards of a prince. Those are fun for a few sessions, but then you hit a wall. You can't do this because it is X that does that, you can't kill X because it is Y who kills him, etc.
I had this playing Pendragon too & I did not like it, though it was one of many things I did not like & I quit. I'm not sure it would have been enough alone though but it's something I would avoid for a protracted game.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.