[Question]{.underline}: What is to be done if a priest suddenly falls sick or dies, and is unable to complete his Mass?
[Answer]{.underline}: The answer to this question is given in the section of the Rubrics of the Missal that treats of the defects that can occur during the celebration of Mass (X,3). The important distinction is whether or not the priest has said the words of consecration. If not, and the priest cannot continue, then the Mass is to be left incomplete. However, if the priest has completed the words of the consecration of the Sacred Body, or both the Body and the Precious Blood, and he cannot continue, then the Mass must be completed by another priest. In the case in which only the Body of Christ is consecrated, then the Blood must be consecrated also that there be a true sacrifice. In the case where both species are already consecrated, then another priest must complete the Mass for the sake of the integrity of the sacrifice, starting where the incapacitated priest left off. In such a case, the priest who completes the Mass will receive Holy Communion under both kinds. However, if it is possible for the priest who fell sick to receive Holy Communion, then he should divide the large host and give half of it to the sick priest who performed the consecration.
The rubrics do not foresee the situation in which there is no other priest to complete the Mass. Consequently, it is a situation that is to be avoided, inasmuch as it is possible. A priest who is alone ought not to attempt to celebrate Mass, when he doubts that he may be able to complete it. If it still happens that a priest recites the words of consecration of at least one species, and then becomes incapacitated or dies, then the Mass ought still to be completed, even if it is after an interval of time, either by the sick priest when he recovers sufficiently, or by another priest, who is asked to come specifically for that purpose. In the meantime, the sacred species should either be left safely on the altar, or carefully placed in the tabernacle until the Mass can be completed.
Answered by Father Peter Scott, SSPX.