Bingowings said:
A friend of mine, who really should join up for here suggested that the body dissapearing thing should be to be an act of will.

Ben when he is cut down by Vader knows he is going to die and he knows the correct meditiation to maintain his consciousness and return to the physical world via the Force. The same is true of Yoda.

Qui-Gon and Anakin don't know the currect procedure but learn it in the afterlife because there is a need to return.

Qui-Gon needs to help the last two Jedi fix the situation caused by the rise of the Sith and Vader needs to continue his redemption by helping the last Jedi rebuild what he destroyed.

That's a good explanation but I don't know how that could be put on screen in a way that doesn't sound (if you pardon the pun) forced.

Conceptually, I really don't have a problem with Qui-gon or Anakin disappearing into the force. The bigger problem is to have it work on screen. Anakin isn't around to see Qui-gon ka-bobed, so as Vader he can still be surprised when Ben disappears. The only problem is the funeral of Qui-gon. Is there any information that is absolutely nessecary to keep? I think the 'rule of 2' can go, it was never really brought back up in the rest of the movies. Anakin's getting trained by Obi-wan can also be cut with the funeral. Yoda delivers this information in the next scene anyway.

If you can cut the funeral, there shouldn't be an issue of Qui-gon disappearing.