I roleplayed with a few people in guild chat but also in the gm hosted events.
Generally we just played off of each other's personalities. You kind of gotta build that and a little backstory that could fit into already known lore though.
I did not do a ton of monster fighting when roleplaying, as most monsters tend to be aggressive in the game at high levels making it hard to converse and build story. That is not to say it cannot happen, it is just harder.