RE: Need Help With A Hypothetical Scenario/Situation/Scene

#2
I mean how MC responds is pretty much entirely up to you, since you're the one who knows what sort of "alignment" the MC has, for lack of a better word. Also it's not clear how personally responsible the MC is for the building falling on the city which adds to the moral dimension. Like if the MC just happens to be in the building and it just happens to fall and kill a bunch of people than his reaction will range from indifference (if they're a "evil" coded character) to like paying lipservice to feeling bad (if they're "neutral" coded) to legitimately feeling bad and maybe even having PTSD or something (if they're "good" coded).
But then if the MC had to actively do something to make the building fall (pushed a button or something) whether he knew the building falling would be a consequence or not - it adds to the dilemma. An evil character might be happy to kill people, a neutral character would be unhappy, a good character might be like legitimately torn up and emotionally destroyed.

The inhabitants of the destroyed village are much easier. Either anger or fear, probably both. Lean harder on one or the other depending on how "violent" or militaristic" the setting is. Like a bunch of peaceful farmers will just be afraid. A bunch of men who returned from the horrible war that happened two years ago will probably be angrier and more prone to violence. Obviously in the like immediate bomb dropping moment everyone will just be terrified though.

Third perspective is again up to you. If there is an authority figure present (like say there is a military fort nearby because the country is at war with the nearby Land of Baddies) of course they will be unhappy - maybe they'll demand reparations or something, probably they'll just go straight to "off-with-his-head" with our mass murdering protagonists. Of course you can just as easily justify there *not* being any particular authority - in real life medieval times its not like there were police forces running around or any particular authorities to respect beyond local lords and whoever had soldiers around.
Which is why I say it's up to you, you can write it either way and have it make sense depending on your setting. Having or not having angry guys with swords around confronting the MC immediately after he steps out of the building is really just a function of how adversarial MC's first encounter with the locals is going to be. And how adversarial the setting is to the MC is up to you as the author, depending on what kind of story you're trying to write.
~writing is hard~