from what i remember, you don't even have to have ditched kael- he gives illidan willing recruits during outland, which would be hilarious to play with if you think about it

just wake up after the timeskip like "i wonder what happened to our prince- wait what do you mean he turned evil???"

it's sad to hear they didn't try adding anything in a book or something as to how nelves got into the illidari. it's such an irrelevant detail but it bugs me none the less