I feel your pain OP and I am sorry this has happened to you.
We were in the exact same position as you 10 years ago. All packed up, kids looking forward to their new schools, our dream house by the sea and the night before exchange we had the rug pulled out from under us. It was beyond devastating. The new life we had all been looking forward to was gone, just like that, in one phone call.
It is honestly the cruelest thing to do to someone but we were angry because this didn't just affect me and my DH, but the kids were devastated too.
We did get our happy ending though. We went back on the market, but it took another 6 months to sell again and then another 3 for the sale to go through. We ended up finding a house nicer than the one we were originally going for, in an amazing village with a great school. The kids loved it and we have never once regretted moving to where we did in the end.
So there will be a happy ending for you too, even though it doesn't feel like it right now. I look back at that time and that house and I know now that it wasn't meant to be. I feel like we were never meant to go there, we were meant to be here, where we are now.
One day you will look back at it and be glad that it happened.
Pick yourself up, pat yourself down and get back on the market.
Good Luck finding another buyer.