Season seven will move forward without the voice behind its titular characters
kotaku.com
Roiland hasnt written anything since Season 1.He did do a lot of improv but thats all after Season 1.
Harmon has always been the one with the juice in the industry out of the two. Hes not letting it go. Especially with the sucess and audience it has.
Rick and Morty has a team of writers serving as a vehicle for Roiland/Harmons vision for the series.
They not only understand the formula of the show after 6 seasons, they had more to do with what its become than Roiland or Harmon.
As far as the voice goes, its well established down to the speech patterns. Its become one of those pop culture things where virtually everyone who's a fan has a Rick or Morty. There's plenty of professional voice actors or impressionists who can do it.
Roiland said in a Vanity Fair video that even Harmon does a solid, convincing version.
Roiland is going down. The ship isnt.
Rick is in his Heaven and all is right in the world.