Banning them during the game would not really be a great choice. First, because that would mean the IFS was working without a report filed. That would hurt 5 man groups that are having fun together. Second, because playing 4v5 isn't fun.
So, for the period from when they start flaming till the end of the game, every potential punishment functions exactly the same. Permaban, ID ban, finding their houses and burning their computers; that'd all be functionally the same during the game. Punishments will happen after the game. With that as a basis, we have to decide how to act during that time. I've decided to mute them in my games. There's no reason to listen to them. In effect, you hold the key to stopping their flame instantly. Press TAB to bring up the scoreboard, and there are 3 mute buttons by each portrait. Mute Chat, Mute Pings, and Mute Emotes. Click em.
Insulting others is against the rules. Report them after the game.