Probably an edit out there but I'm just guessing.

Grievous is a McGuffin but a good one for me at least. I think some of edits of the PT fall down IMO because they follow the "If it can be cut... cut it" philosophy. If you follow that logic you could cut most of the middle out of ESB since essentially the Falcon p*sses about waiting for Luke to walk into Vader's trap. Han could just fly the Falcon straight to Bespin but then you'd lose all the fun and character of the piece with it.

I can't see any major obstacle to being able to remove GG if you wanted to, in terms of narrative. As long as it's possible to do dialogue trims that reflect OWK going off to end the federation war, rather than to kill GG. But I can see several major scenes in my cut that are essential to character development between Obi and Anakin that would have to also be removed, fatally damaging the film.

I also think having another "Baddie" like GG helps deflect attention away from the importance of Vader in ANH. In my cut Anakin does not become Vader so the surprise is saved for ESB. Having a parade of villians like Maul, Dooku, Greivous, and Tarkin who only survice for basically one film suggests that Vader is just another in line (Though clearly the best!).