The fact that he thought it might become necessary to conclude that the See is, in fact, vacant means that he also thought something most who accept the V2 popes do not want to accept:
It is possible for someone below the Supreme Pontiff to conclude such a thing is true within the order of fact -- and to do so before Holy Church has made a decision within the order of law. Otherwise, it was completely meaningless to even say what he said.
Like it or lump it, it is crystal clear that his thinking on that point is completely at variance with the vast majority of those who claim to see things as he did.