Free will is something where people talk about it as a binary thing, but it can be both the ability to make choices, yet very deterministic at the core. If someone asks you to think of your favorite color, in your mind you visualize what that is, and it's your preference and choice for whatever reason you like it best. But the deterministic part begins when you wonder when you made that decision. Can you even narrow down the instant when it popped into your mind as the preferred choice, or what occurred before it was made? At some point there was a triggering of thought and memories from the question asked that resulted in you thinking of your color, but when did it go from predictable neuron firings to a choice? There is a gray area there.
For what it's worth, while I enjoyed some of the later Terminator movies for themselves, the saga ended with T2 in my mind. Where that future led could be just as dark, as someone else could come up with their version of Skynet eventually, like any other technology, but we are left to ponder that on our own. The actual previous future is gone thanks to the efforts made, and we're allowed to try again.
It's hard to let them go, but they have to live their own life, and you hopefully did the best you could to give them the tools they will need to succeed. Look at it this way, making such a move early in life lets them sample what else is out there, and no reason they can't either come back or move on to something else entirely, now armed with two different culture experiences. So much better than being trapped in one place or maybe worse, settling for that, and not see other places at all.
I guess the real question is why is he making the choice. Current conditions in the US? Her? A bit of both? Or maybe he's gotten a sample of AU and likes what he saw. As long as it's a good reason(s), and they all are, then why not?