for what it's worth, the buildings were all empty. it was a pretty great episode because the whole time superman looks insane and extremely paranoid and you genuinely think he's lost it a few times. basically lex built this "city" within metropolis and was unveiling it to the world. it was supposed to be this utopian place where everything was free and it made lex look like an amazing humanitarian. i don't remember exactly what his plan was, but that generator or whatever it was that superman was after was obviously extremely dangerous and illegal and all kinds of bad. it was during that phase where lex was on his run to become president (i don't think he ever got there in the show, but it was inspired by that run in the comics) and everyone thinks lex is this amazing guy and really only the justice league know what's really up.
so yeah, the only people in that area they destroyed was the people they showed. lex, superman, captain marvel and a few press. so no one died but you get to see superman destroy a bunch of property which feels very out of character for superman, but it was all lex's property so he was fine with breaking it all.