Whoop Whoop

I heard from a source that Obi-Wan became one with the force in a way at the very moment he was struck. So to sum it all up, Vader never really killed him. But don't take my word for it.

Also thank you lol

Ok that makes sense

The way I've always heard it:
Masters of the force don't leave a corpse when they die, they get to be one with the force. Don't ask me why they don't, maybe they have to go in soul and body, maybe it's something else... The point is, Vader's strike kills Obi Wan, therefore producing his fusion with the force. If he had just cut his hand off, we would be seeing something totally different.
This was the original trilogy lore, with Obi Wan and Yoda's body dissapearing upon death, and Anakin/Vader potencially doing the same (and only the suit/armor remaining in the pyre by the end of the VI episode).
But then of course along came Lucas, and shitted on his own universe lore with the episodes I II and III.

Ok so if they're masters of the force if it's a killing blow they become one with the force if otherwise it'd dismember them like Luke's hand or leave a body, Sweet thank you

Almost that. Masters of the force theorically NEVER leave a body upon death. Yoda dies peacefully, yet his body dissapears like Obi Wan's to fuse with the Force. But any injury, not causing death, would be producing no special effect that we know of. It just happens that if the injury causes the death... boom. Instant dissapearing.
Also, apparently this doesn't apply to Knights (or apprentices), only to Masters. Luke only a Knight by the end of episode VI.
And anyway, keep in this mind this is canon for the original trilogy (and most of the expanded universe that was based in it), but then Lucas started the other movies, and shitted on his own lore.