Yes. Many people have died without receiving the last rites (e.g. those who die in wars, car accidents, etc.). God is not bound by his sacraments (CCC 1257). And, “since Christ died for all, and since all men are in fact called to one and the same destiny, which is divine, we must hold that the Holy Spirit offers to all the possibility of being made partakers, in a way known to God, of the Paschal mystery” (CCC 1260).
Thus, you need not despair of the salvation of your brother. Pope John Paul II in Reconciliatio et Paenitentia (Reconciliation and Penance) offers us these words of comfort: “Moreover, God in his merciful love is greater than our hearts, as St. John further teaches us, and can overcome all our psychological and spiritual resistance. So that, as St. Thomas writes, ‘considering the omnipotence and mercy of God, no one should despair of the salvation of anyone in this life’” (17). Continue to pray for the repose of his soul.