I look at it this way if it's a natural death or if it's an instantanious death then you disappear. but for quigon and all the other jedi he hadn't learned how to become one with the force yet, till he was dead
Qui-Gon seemed to have a better understanding of the Force than prequel Yoda. It interesting that in the prequels Yoda focuses on the future but in the OT he realized like Qui-Gon that the present was just as if not more important than the future. Basically Yoda changed his views on the Force between the trilogies, and this makes sense because focusing on the future did not help the Jedi in the prequels.
If Yoda dies before Jinn, then the events of the movies would not necessarily transpire as they have done so I'm quite sure Yoda eventually would have managed to find out about retaining one's identity the way Jinn did.
McCallum said that Anankin did disappear, just that we didn't see it. That only the armour was burnt.
Now, this again goes wrong on so many counts: OB1 and Yoda took a while to learn the disappearing trick from dead QGJ... Anakin did it in a couple of minutes on his own. But prolly the idea that he is the Chosen one means he can do anything.
The plotline is so stupid and so badly worked out that is hardly worth debating. Especially since the PT makes these problems and kinda muffles it away in a corner. I don't see any logic or reason or any consistency in the whole ghost thing...
I must admit the PT did ruin a lot of perceptions I had about the Jedi in the OT days. I assumed the force ghost thing was something every jedi could do. It didnt really need more explanation, until TPM when Qui-Gon didnt disappear. Not sure why Lucas did that, just to give a quick explanation right at the end of the PT.
Also the whole perception of the force like "size matters not" and "the ability to destroy a planet is insignificant next to the power of the force" were kind of ruined in the PT, when they showed just how limited the powers of the Jedi are. Making those classic OT lines make no sense at all!
The point of of how Anakin suddenly learns how to fade into the Force is weird... It was never weird, it was never a point until the PT. Now I guess we all just have to assign it to the prophecy, that the fact that he is the chosen one, he can disappear as well...