Did Banon and Arvis die?
as far as i know, its never said. but i havent saw them.
theres a very high chance they died, but does anyone know for sure?
I'm pretty sure they die. We don't see them in the World of Ruins. But according to the Wikia, Sakaguchi didn't want to answer about Banon's fate and said that he wanted the players to "use their imagination". It says nothing on Arvis though.
Ya like Shiva said, we are left to use imagination. However they disappear when the continent begins to float so I am guessing that is when they died.
I always assumed the died. In terms of story, Bannon may have been a leader, but he was only important for that one segment where you couldn't let him die. Arvis was more underground. They basically chilled at Narshe and eventually at Vector once the Empire claimed they were done going on the war path. However, when the party escaped, only playable characters came with. I can't remember if Arvis and Bnnon can be found after that, but maybe they were killed by the Empire?
Otherwise they were straight up killed when the world slid into ruin. Since they aren't around at all I say they are dead.
I mean, the reality is that the minor characters served their story purpose, so they were subtly written out of the narrative since the focus of the game changed from a political conflict, to a supernatural conflict, then to a worldwide conflict/rebuild/resolution.