I feel as if this was made with "the skill will be gone" regardless of if the function is used somewhere else- or if the move just changes as we know it.
As in
yeah dark arts as we know it now may be gone, but is it still there as a skill with a different effect? Or is the effect given somewhere else?
Without knowing anything about what they mean by 'gone' I just kinda chalk this up to a fat shrug.