Someone else takes his place. Someone less awesome.
In 5 he just cameos as a performer -- the focus of the scene is to overhear a meeting of some bad guys.
In 7 he leads a crowd to the party's ship as they're about to leave on a mission. There's a mer-fey named Beshela who wants to screw with the party's ship, and another fey named Copperhat the Headless wants to keep the party around. Copperhat leads Rock to the party's ship in order to have an audience and deter Beshela's hostilities. Afterward he brings Rock with him back to the Dreaming. If Rock isn't around, you could just have Copperhat do something similar to Thames Grimsley, but not take him to the Dreaming.
In 9, Rock is 'murdered' to provoke a civil war among the fey in the Dreaming. If Rock isn't around, you can just create a new fey, someone who was beloved by both sides of the conflict. Maybe there's an NPC the party knows who you think would work well here; if so, lay the groundwork to get him into the Dreaming by adventure 7.
In 12, Rock is still in the Dreaming and can assist the party on their adventures, but he doesn't play a plot-critical role.
Rock is mostly flavorful zaniness. He's not a major player.