What you really need to ask yourself is do you like Roiland OR do you like the show. Sure, Roiland is the co-creator but the show is mostly ran by Dan Harmon and the writer's room now more than anything Roiland does, and he pretty much comes in for voice work since he's been doing way too many other projects to really have a hand in shaping the narrative of R&M, which is again mostly Harmon and the writer's room now. Voice tech is also at the point where anyone can sound like anyone and even in South Park Matt and Trey don't do the voices anymore as voice technology changes their normal voices into their characters as it was shown in a short documentary they released, which is on YouTube. The cadence is the only thing that could be an issue with Rick and Morty's performances, but surely there's a super fan or two out there who can replicate the cadence of Rick and of Morty perfectly. All this being said, of course, is if Roiland is found guilty and cannot continue with the show.