It is easy to see why many would feel they are wasting work if they have spent a lot of time creating a scene and then not having it come to pass because of player choices. Yet, the principle of the Quantum Ogre states that you should indeed do just that.
So. Are you indeed wasting work? The curious thing is that before having read about agency and the Quantum Ogre, I thought that I was, so I made shure my players always where exposed to my orchestrated scenes one way or another. In short, I was an illusionist and a railroader. But at the same time, I was spending an enormous amount of time working out elaborate background stories for my games that very seldom came into play in a very significant way.
I think this perspective is a good way to get around some of that resistance to agency i RPG's. Creating backstories like that, and creating elaborate scenes is part of the fun of DMing. So what if the players were to late to witness the inidious offering to the Snake God! So what if they were too late and came in there after it happened! So what if they chose another way in and managed to prevent the whole ting!
In those cases, the scene you have created is part of the backstory. It has still happened, even if the PC's didn't witness it.