St. Augustine, in his book, "The Manual of Faith, Hope, and Love", speaks of the God's marvelous providence for those who walk "the road that leads to life":

"Because of their wicked pride some angels forsook God and were cast down into the deepest darkness of this sphere from their celestial dwelling place on high, but the remaining number of angels remained with God in eternal beatitude and sanctity.  These angels were not generated by one fallen and damned angel so that his original evil bound them by the chains of a vile succession so that he might draw them all to deserved punishments, as is the case with men [affected by original sin].  But when he who became the devil was raised up in his pride with his wicked comrades, and in his pride was prostrated with them, the rest of the angels adhered to The Lord in holy obedience, receiving that which the wicked ones did not have -- certain knowledge by which they were forever assured of their stability, never to fall.

"Therefore, it was pleasing to God, the Creator and Governor of all things, that because the whole multitude of angels did not perish in their rejection of him, those who fell should remain forever in their perdition, but that those who persisted with God during that rebellion should rejoice in their most certain knowledge of their ever-happy future.  But his other rational creature -- mankind -- which had perished in sins, both original and personal, as well as in their punishments, would be repaired by him and would make whole again the number of the angelic company which had been lessened by the diabolical ruin.  For this is the promise made to the risen saints, that they would be equal to the angels (cf. Luke 20, 36).  In this way, the heavenly Jerusalem, our holy mother, the city of God, shall not be defrauded of  the multitude of her citizens, nor shall she perhaps rule over a greater number."

That is, the exact number of places in heaven lost by the fallen angels will be taken by the risen saints, who will number neither more nor less than the fallen angels.