What if the Romans hadn't killed Jesus?

[Tonus]

Did the Romans have any free will in the matter, given that this 'sacrifice' was supposed to be Yahweh's plan for humanity?

Almost certainly not, based on Yahweh's actions in the Bible. He is willing to compel people to act or not act (ie, hardening Pharaoh's heart) in order to get the results he wants. If you consider the possible consequences of certain stories if they had turned out differently, you realize that they had to turn out the way they did.

Or maybe not. What if Yahweh were shown to be wrong? What if Jesus had accepted any of Satan's offers in the desert? What if Job had gotten angry or despondent enough to curse god? Does god disappear in a puff of smoke, taking the universe with him? Or... does he just wipe off the chalkboard and start over? Humans are made in god's image, and we make mistakes. We have the ability to learn from those mistakes and turn out better work. Why wouldn't god be the same? Why insist on the idea of perfection?

If any of those "tests" could have failed, then the Christian has to consider the possibility of failure on god's part, of his fallibility. If they could not have failed, then they were really just a con. God was having us on, possibly for his own amusement, possibly out of some need to be recognized as a hero, which might be a more frightening possibility than that he is mistake-prone. A 'perfect' being who craves attention to that degree is the kind of person who... would torture people for an eternity for not doing so.