When you speak of "The Needs of the Time", I would say that, in truth, there is nothing about republicanism per se that makes it unsuited for times when monarchy has held sway, or vice versa. Rather, government's success or failure is determined almost entirely by the personal qualities of the leaders who run it.
Are you saying that brilliant emperor of the 2nd after Christ century could have restored the Roman republic or that brilliant consul of the 2nd century BC could have become king? I doubt it.
To every thing there is a season, and a time to every purpose under the heaven:
A time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted;
A time to kill, and a time to heal; a time to break down, and a time to build up;
A time to weep, and a time to laugh; a time to mourn, and a time to dance;
A time to cast away stones, and a time to gather stones together; a time to embrace, and a time to refrain from embracing;
A time to get, and a time to lose; a time to keep, and a time to cast away;
A time to rend, and a time to sew; a time to keep silence, and a time to speak;
A time to love, and a time to hate; a time of war, and a time of peace.
(Ecclesiastes 3)