As you can see in the gallery below, he would have appeared as a Force Ghost, with his appearance alternating between his Light and Dark sides (a smart decision considering the fact that having him find redemption for all of his terrible actions by saving his son at the end of Return of the Jedi felt like something of a cop out). This version of Darth Vader was likely going to appear in earlier drafts of the script when Luke had a more significant role.
That obviously raises the question of whether or not we’ll see this idea utilised in Episode VIII! If I had to hazard a guess, I would imagine we will, especially after some of the big reveals in The Force Awakens. With the right direction and a relatively small role, Christensen could have the chance to do something really interesting here, and with rumours pointing to Vader showing up in Rogue One, chances are we’ll see him soon enough!
In other Star Wars gossip, it’s been revealed on Twitter that the original title for The Force Awakens was Shadow of the Empire, the same as a very popular EU novel from the 1990s. Better or worse than what was ultimately chosen? We’ll let you decide on that below.