There would be two reactions, one for the kids and one for myself.
First, my kids love her, adore her, and she loves them. Even though I disapprove her way of parenting over which I have had to many fights with her, I would be truly sorry for my kids if dw decides to leave them.
Second, to be honest, I would be happy to be relieved from a husband-and-daddy role which I have been playing since meeting her a long time ago. I still love her just like a brother would love a sister, but we see the world differently, and though I am still physically attracted to her, she hasn't been to me for a long time. Though I suspected she had an affair last year, I didn't even bother to find out. I was living in an emotional wasteland for too long, though it was partially due to my own fault.