The Jedis Deisappear Because...
Ok - I've thought about it...and here it is....beyond a shadow of a doubt...why some Jedis disappear and some don't
THEY HAVE TO ACCEPT THEIR FATE
***Qui-gon didn't...and I guarantee you Mace won't...or none of the other Jedi we see killed by stormtroopers or Sidious.
***But Obi-Wan did...and so did Yoda.
-I bet you that it's an old Jedi belief that those who accept their fates shall be able to retain their spirit for some time. How many Jedi deaths do you think Anakin had seen growing up, or even after becoming Vader that were natural deaths?
Obi-Wan's is the first...that's why he kicks Obi-Wan's robe...
It makes perfect sense.