Honestly, Roy would be down for helping to negotiate a ceasefire, even if he thinks the King is batshit and the Princess is pretty naive. He's a sucker for happy endings, and preventing death is his main objective. So if Hank wants a buddy, he'll happily help.

Roy also has the power of hypnotic persuasion to convince people that they really should not kill each other, though he doesn't really like to use it unless he absolutely has to.