Of course he's outside the Church, UR, your obfuscations and distinctions notwithstanding. If he denies the authority of the present pope, he denies papal authority.
He's a Protestant.
Wrong. You must believe someone is pope before you can be schismatic. If you truly believe someone is not the pope, but affirm papal authority nevertheless, there is no schismatic intent.
In the early fifteenth century there were once three claimants to the papal office and each had his adherents. Were those who denied the authority of the other two claimants schismatic? No.
According to the Catholic Encyclopedia, "under these circumstances good faith may, at least for a time, prevent a formal schism; this begins when the legitimacy of one of the pontiffs becomes so evident as to render adhesion to a rival inexcusable."
So good faith is the key. So also is the self-evidence of the legitimacy of the pontiff himself. I personally believe Derksen has been rash--but he seems to me in good faith nevertheless, even as the heterodoxy of this Pope has become more and more obvious.
Can someone please prove to me that John Paul II is the Pope? Since he has promulgated documents and committed acts contrary to Catholic teaching, the burden of proof is upon those who claim him to be the Pope.
Unless one was there when he was elected and one is absolutely sure he has not lost the Faith, I don't think you can prove he is the Pope.
I wouldn't be so quick to dismiss sedevacantism. One can bury their head in the sand an wish it ain't so, but that doesn't change the facts.