Canon 682: The laity has the right to receive from the clergy the spiritual goods and especially the necessary means of salvation, according to the rules of ecclesiastical discipline.
Unam Sanctam, Boniface VIII, 1294-1303: “…we declare, say, define, and proclaim to every human creature, that they, by necessity for salvation, are entirely subject to the Roman Pontiff.” (DZ 469)
Since it is necessary for salvation to be subject to the Roman Pontiff, then we can reason that it is necessary to have a Roman Pontiff to be subject to.
Canon 682: Laici jus habent recipiendi a clero, ad normam ecclesiasticae disciplinae, spirituali bona et potissimum adjumenta ad salutem necessaria.
Unam Sanctam, Boniface VIII, 1294-1303: Porro subesse Romani Pontifici omni humanae creaturae declaramus, dicimus, definimus et pronuntiamus omnino de necessitate salutis. (DZ 469)
Since it is necessary for salvation to be subject to the Roman Pontiff, then we can reason that it is necessary to have a Roman Pontiff to be subject to.
Canon 682: The laity has the right to receive from the clergy the spiritual goods and especially the necessary means of salvation, according to the rules of ecclesiastical discipline. 
