Have you seen how fast Yoda moves? All he would have to was get out of Mauls his reach to kill Grievous which probably wouldn't take him that long...
We all know Yoda was superior to Dooku who was superior to Grievous, and there for Grievous would get his ass kicked in a few seconds, if not by the use of the force then by other quicker methods.... Then there is just Maul left, and yes i'm pretty sure Yoda can keep Maul away long enough to finish Grievous off...
In that case the two would fight and Yoda would win, if they could stick together the entire time, Yoda would probably lose. But Yoda isn't stupid one succesful force push against Maul and Grievous is dead... Devide and conquer is the key here
Grievous, weakness- Half droid. Solution- crush the insides of his foe. Maul, weakness- Overconfidence. Solution- lead on that he is winning then strike when he feels the match is his. Solution to battle- Destroy Grievous from the insides while maul is approching yoda. When Grievous is down yoda will have a one on one battle with maul. Maul will put on a very difficult duel but it may be to difficult to take yoda on his own.starwars