Yes, I do believe that CeeLo Green leaving the Voice will negatively affect the show's ratings. CeeLo Green was one of the original judges and has established a fan base. Some are very attached to the artist as a Voice judge. These people may decide to not view the show because it has changed. Many people do not appreciate change.
CeeLo Green is extremely overrated, and the new judges they have in Usher and Shakira are so much better than he will ever be. Usher and Shakira are pop icons, while CeeLo has only been on the scene for a mere decade or so. Usher and Shakira, the replacements, will bring the raings up.
I do not remember hearing about the ratings for the show going down the last time he left. Of course, I do not really keep up with ratings. I am sure I would remember if it drastically effected the show. I think the show is just getting a bit old and if the ratings go down, it will be because of that. They seem to pick the same type of singers every time to win the show. That is why it is starting to get old. Same old style of singers and nothing different.
Cello contributes to the voice, but with star quality counter hosts, is not the only star. Thus creates argumentative quality between the hosts of the show. Summing inadequate judgment for a solo appraisal of show quality. Hired to hedge risk for amateur tours of skill and arts, based on vocal solos. Exposing contestants to social revaluation and possible failure.
When I have watched the voice, I never really did like CeeLo Green on it. Adam and Blake always seemed to be like the headliners on it. Also they have proved that they can fun the show without him when Shakira and Usher took over for him and Christina Agulara. The show will be fine, if not more that fine.