If you think about it, Obi-Wan and Yoda also gave themselves over to the Force in a similar fashion, especially since Obi-Wan disappeared an the moment before Vader’s saber hit him.
Did he? I always thought Vader killed him.
yeah he did. vader’s blade never even touches him.
“If you strike me down, I shall become more powerful than you can possibly imagine.”
Emphasis mine.
Yeah, Vader kills him. But he gives himself up to the force by allowing Vader to kill him. The two aren’t mutually exclusive.
His robe being “empty” before Vader strikes him is definitely a limitation of the special effects of the time.