You may wonder if Yoda disappeared after dying, why didn't Vader after dying in this 1983 film
In the movie you can't see 
whether Vader's body is in the armor or not when it is ... Darth Sidious, and upon 
his death, the spirits of Kenobi and Yoda completed his training .... why Jedis 
ghost, how they died, who disappeared and who didn't, have definitely... [DOC] [TLE] How 'Return Of The Jedi' Ruined 'Star Wars' Forever | IndieWire [PAR] May 24, 2013 12:00 pm .... Everything in the 'Star Wars' universe following '
Return of the Jedi' would be patterned after what Lucas established in that film.