I’m of two minds on this. One, if Critical Role came out with their own RPG it would eat D&D 5E’s lunch. Because the majority of the resurgent interest in D&D is from CR. The fans who disliked 4E came back for 5E, but 5E wouldn’t have lit the world on fire as it has without CR. Two, it would put a small but noticeable dent in D&D as CR has made avid fans of D&D from the avid fans of CR. The Call of Cthulhu one-shot CR did had a huge positive impact on Chaosium. CR could do quite well with an RPG of their own, but I doubt it would be more than a few percentage points off WotC’s sales.