"We declare, say, define, and pronounce that it is absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff." (Boniface VIII, Unam Sanctam).

If you accept that as it is written, how can a person be saved if they die during an interregnum?  

"And this translation, since the promulgation of the Gospel, cannot be effected, without the laver of regeneration, or the desire thereof, as it is written; unless a man be born again of water and the Holy Ghost, he cannot enter into the Kingdom of God".

How can a BOD cannot save anyone when even justification cannot take place without the sacrament, or the desire thereof? - how can a BOD save anyone when it cannot even justify anyone? 

2 more questions for you to ignore - or to post volumes from fallible saints and fathers against this infallible decree.

"And this translation, since the promulgation of the Gospel, cannot be effected, without the laver of regeneration, or the desire thereof, as it is written; unless a man be born again of water and the Holy Ghost, he cannot enter into the Kingdom of God".

How can a BOD cannot save anyone when even justification cannot take place without the sacrament, or the desire thereof? - how can a BOD save anyone when it cannot even justify anyone?

2 more questions for you to ignore - or to post volumes from fallible saints and fathers against this infallible decree.

You didn't answer the question I asked.  Let's give it another try:

"We declare, say, define, and pronounce that it is absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff." (Boniface VIII, Unam Sanctam).

If you accept that dogma as it is written, and (supposedly) without interpreting it, as you claimed, how can a person be saved if they die during an interregnum?  

There are two requirements for subjection to the Holy Father:

1) material:  Baptism.  Trent teaches that only the baptized are subject to the Holy Father.

2) formal:  intent to be subject to the Holy Father (which is why schismatics are excluded, per Bellarmine).

Neither of these ceases in a sedevacante period, nor did they cease during the Great Western Schisms for those who happened to pick the wrong pope.

There's no requirement that there be an actual body in the See of Peter.

This is actually a serious reason why that EENS definition militates AGANST BoD, namely, Trent's clear teaching that only the Baptized are subject to the Holy Father and his jurisdiction, to the exclusion of catechumens.

Just as with the Sacrament of Baptism, infants aren't required to have the formal intent to be subject, since they are incapable of forming it, but are subject merely by virtue of their Baptism.  And that is why baptized schismatics who die before the age of reason are considered to have died as Catholics.