There is no such episode. Is it possible, that you are thinking of Cartmann, and not Kenny? Because that scene does exist.
He is Kenny
Yes Kenny is Mysterion as revealed in the episode "Mysterion Rises".
Kenny dies
And Kenny always lives in the episodes after he gets killed. Dude.. It´s South Park..
The scene where Stan sings about Wendy is actually in the South Park movie. ("South Park: Longer, Bigger and Uncut")
In Season 5 Episode 13 of South Park Kenny Dies.
they sort of make up in the episode "the list"
ANSWER:They did. You know, them. As quoted from one episode. "OMG! They killed Kenny! You bastards!"
In Season 4 Episode 15 Fat Camp.
There isn't an episode with Ray Mysterio in it, but Kenny dresses up as Ray Mysterio in the episode W.T.F.
They usually have regular talks or whatever but they break up in the episode Raisins.
yeah in chef goes nanners season 4 episode 8