St. Augustine The solution to this problem, suggested St. Augustine, was to see how those fallen angels could be, and would be, replaced by humans: https://www.patheos.com/blogs/henrykarlson/2016/04/replacing-fallen-angels-overturning-the-evil-powers-part-1/
Anne Catherine Emmerich (1774-1824): “Man was created to fill the choirs of the fallen angels. Were it not for the Fall of Adam, the human race would have increased only till the number of the fallen angels was reached, and then the world would have come to an end” (Life of Jesus Christ and Biblical Revelations, Vol. 1, p. 17).