OP, I get the feeling that what you really want, is for this just to disappear, and you carry on, with you being very happy in your life, him not so happy in his, and everything stays the same. This opportunity never came up for you as a family to have to make a decision, whether to go for it, or for him to give up on it, to regret and mourn it. That's not possible.
Just because we were a particular way when we met at university, doesn't mean to say we never change - whether that be in job, focus, or a new yen for the different.
As an ex-pat wife, part of my job, as I see it, is to support my DH's job, as that is what facilitates our family lifestyle. Obviously, you work part-time, but your DH's job is still what primarily facilitates your family lifestyle. I'm an introvert too, and don't particularly enjoy socialising, but I do realise that a bit of it really helps with DH's work, so I do it. Perhaps, you could make it clear that this is not on the cards for you if you did move.
It does take a degree of flexibility, adaptability and resilience to shift countries, particularly with children, and a combined enthusiasm or determination to make it work. If you haven't got these, then you haven't got them, and that's all there is to it. It would be very unlikely to work, if you aren't prepared to make it work.
But there is going to be an opportunity/benefit cost, whether you go or whether you stay, depending on just how much DH hates his current role, how hard it would be for him to find a comparable opportunity here, and how detrimental it could be to his career, which you liken to a vocation, in staying here. That could potentially impact on your relationship, and potentially on your lovely life that you like so much.
There's risk either way, as I see it.