You can do the majority of this game's content without a full breakdown
But everyone still has to know their role and the fight down pat. If they screw up, coordination goes out the window, healer goes OOM or draws aggro, the tank dies, everyone dies, wipe.

You don't need to do changes on the fly mid-battle unless something goes wrong (and thus make voice chat not needed), boo hoo hoo. Cry me a river.