Hi, and welcome!
I have a four year old as well, and she and I just moved over here to live with my husband. Her father was originally planning on joining us here via the highly skilled route, but he changed his mind about moving for now (possibly in the future, or maybe we'll move back to the states; we'll see).
She's adapted totally well to the distance. I felt pretty guilty about it, naturally, but she's happy and they get to Skype chat once or twice a week. At four, they're old enough to understand that mommy or daddy is away for a while but that they still love them very much, and that they'll get to see them soon. They're also young enough to be easily distracted, and unless your son is so attached to you that you can barely drop him off with another caregiver, he should be fine for a little while.
If it's just a month or two, I would say give it a go. Honestly, at his age, you'll probably suffer from the separation a whole lot more than he will.
Good luck! I hope you get it sorted out.