Despite the desire to have Yoda appear in the prequel, I really wish Yoda had not been in the prequels. I would've preferred that Yoda, even though strong in the Force, realizes that he is too frail, physically, to counter the looming dark side, and thereby, leaves, goes into hiding, waiting for the good Jedi to find him, or at least, wait for one who would be strong enough to train and battle the Emperor.

(And I really would love the surprise of ESB when we finally do get to see Yoda remain intact. "That's Yoda?!" As it stands, Yoda is ruined for me by having him appear in the PT. Now it's no surprise to anyone by ESB).

So, we'd get exposition right away in Episode I of Obi-Wan bringing Anakin to Yoda, only to be told, "He's gone, no one knows where he went. He said he wasn't strong enough." And then Obi-Wan decides, "Okay, if Yoda isn't here to train him, then I will."

Which fits right in with everything Obi-Wan said in the OOT.