Fear not Art! I have it on good opinion you don't even have to be Catholic to be saved. So don't be losing any sleep over the Anti-Popes ravings/edicts.
Since it is necessary for salvation to be subject to the Roman Pontiff, then all who die between the death of one Pope and the election of another, are damned.
It’s simple logic!
Even the Catholic Church teaches that you don’t have to be Catholic to be saved.