Baring in mind that Kadaj is one-third of the former real Sephiroth.

I dont think Sephiroth can ever be real again but anyone with JENOVA cells and reunited with anypart of JENOVAS body recreating Sephiroth. Both his and JENOVAs will are the same as in wanting to bring dispair to the planet.

If only Spehiroth had knew the massive mistake in identity Professor Gast had made in his research of JENOVA, none of this would of ever happened. lol