John Doom said:

I read somewhere that, to justify Vader's death in "Splinter of the Mind's Eye", they recently officially said that it was just an image of himself created with the Dark Side.

Actually, no, they didn't go with that idea. If they had, it would have actually been a good way of fitting SOTME into post-TESB continuity without having Luke actually duel Vader prior to Bespin.

What they did was go down the most simplistic route possible and made the Vader Luke & Leia fought in the Temple of Pomojema the real Vader, using some dumbass "the Kaiburr Crystal amped up his anger" excuse for why he wanted to kill Luke despite knowing he was his son.