We know that the plan of salvation was predestinated for Christ was the lamb slain from the foundation of the world.
Revelation 13:8 And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world.
Many things have been predestinated, some from the foundation of the world others later in time. it is certain that the Lord has appointed a day in which to judge the world, but there are numerous things that have to take place before then. Prophecy is a predestination. When God says something is going to happen he is not guessing, prognosticating, predicting, speculating, or foreseeing; he is telling us what he is going to make happen, predestinating.
Amos 3:7 Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets.
The Lord established a blueprint covering a span of time in which to accomplish reconciliation and redemption. Within which was designated along the timeline all that must come about in the course of his purpose. However, within the blueprint was space for man's free will, God's judgments upon man, and even time and chance.
Ecclesiastes 9:11 I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all.
It would seem that there must have been within the blueprint a plan A and B. If man obeyed history would go one way if not another.
For a comprehensive look at the issue of Predestination examine the following studies: