I am about the same age as your wife, and can relate somewhat to your questions about menopause, and also talking to your grown children.
What I get from talking to a lot of women is that menopause affects us all differently. There are no hard and fast rules, except that we do feel that we are different. For me the biggest change is sleeplessness. I'm on these boards all night. For others it's hot flashes, or lowered immunity. Most of the women I know have not had a MLC and had affairs. But it certainly is a possibility. I think many people do stay in marriages they consider unhappy, waiting for the kids to finish high school and put off a break until then. It is possible she has been planning this for a long time. Emotionally she may have packed her bags and checked out of the marriage years ago. Doctors rarely prescribe HRT these days since it raised the cancer risk. So I doubt you would get any help there. Some women take black cohash and soy on their own to lessen the effects of menopause. I've never tried it.
When my husband and I were on the rocks I spoke honestly to my children about it. For 2 reasons. One, that's how I've always dealt with my kids, and I'm not changing it. And 2, because they are adults involved in their own relationships and can benefit from knowledge about marriage. I use every example I can think of from my past to counsel my kids on how to deal with the opposite sex. I don't judge you at all for talking openly with your kids. I encouraged mine to talk to their father about how they felt about breaking up the family. My oldest punched the door to his room til it pulled the hinges from the frame and broke a hole in the wall behind it. He didn't hesitate to tell his father what he thought. The other two were silent. But they all felt that it was their life too that hung in the balance.