Before the events of Star Wars Revenge of the Sith, Grievous and Mace Windu actually meet to fight one another. The battle is one that I wish we got to see on screen in live action, however, at least we got it in this book: Labyrinth of Evil by James Luceno. The book takes place before Revenge of the Sith where it follows the Jedi Anakin Skywalker and Obi-Wan Kenobi on their mission to get the holo chair from Nute Gunray, and track its information down to find Sidious and reveal his true identity as Palpatine.
This all happens before Anakin fights Dooku, and of course, before he becomes Vader. Had Mace beaten General Grievous, I think things would have been very different, because then Obi-Wan would be at the temple most likely when Anakin revealed the truth about Palpatine being the Sith Lord. I think Obi-Wan could have guided Anakin better in that moment, perhaps, or at least it would be down to Obi-Wan and Palpatine surviving, and that's a choice Anakin would have a hard time making. It could have potentially changed Order 66 from happening.
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