On the practical level it still requires a judgment by the proper authorities.
To be BINDING it requires a practical judgment. If it were impossible to assert a Pope was a heretic no matter what he said or did without recourse to "proper authorities" - then it is a situation that is impossible to rectify.
How does your assertion that the pope is a heretic and therefore not a true pope rectify the situation? It doesn't.
God has allowed this crisis for reasons known to Himself. Once the crisis ends, I have no doubt that the proper authorities will judge the post Vatican II popes - and I expect that Paul VI to Benedict XVI will be declared heretics. And if I live to see that wonderful day, drinks will be on me.
A sedevacantist who detests John Paul II and Benedict XVi, may well end up in hell along side of them if he separates himself from the Church, since outside the Church there is no salvation, and the Church exists today just as it did prior to the council. The difference is the condition, not the being itself.
Just as a man dying of Aids is the same man that existed prior to being infected, so too the Church today is the same Church that existed prior to Vatican II. The difference is that today the Church is in the condition of an Aids victim on his last breath. It is just about dead, but like our Lord, it will rise again.
If you leave the Church, or declare it to have become a false Church, you separate yourself from the mystical body of Christ and will get to spend eternity in hell.
On the other hand, if you realize the sick situation of the Church, avoid the heretics within, and leave it to the proper authorities to sort everything out in God's times, you will not risk eternal damnation for separating yourself from the Church.
Sedevacantism is not only a dead end and no solution to the problem; it is probably one of the main traps of the devil to lead those with the Faith out of the Church. It is one thing to avoid the corrupt elements within the Church during this unprecedented crisis (which is the prudent thing to do), and another to declare that the Church itself has ceased to be the Church and then separate yourself from it. The former is prudent, the latter is true schism. There are many victims in the current crisis, and more dangers to sedevacantism than people realize.