Does a priest have to consume the Eucharist no matter the state of his soul?
Can a priest decide not to consume the Eucharist during mass if in doubt whether he is in mortal sin?
The short answer is no.
The celebrant must always consume the sacred host at mass, in which he acted as a consecrator of the sacred species.
Moreover, the celebrant's Communion is ...
A heretical, schismatic, or excommunicated priest can consecrate because (III q. 82 a. 7 ad 3):
in consecrating the sacrament he speaks as in the person of Christ, Whose place he holds by the power of his orders
His ability to consecrate doesn't depend on his being in a state of grace but upon his being ordained; the sacramental character of Holy Orders is ...
Discussing the "Connection of the Gifts among Themselves and with Charity", John of St. Thomas writes in The Gifts of the Holy Ghost:
Sinners living without grace can acutely discern, dispute, and even treat of divine things and of mystical or loving understanding as an object and matter of disputation. But they cannot use such an understanding as ...