Re: SPOILERS AHOY
Sorry for letting you wait so long for my reply but I still tend to see things more optimistic than you do.
A) Hermione and her order friends must accept that they have grown apart in these 6 years, and look from there on how and to what extend they can repair things. I think she explicitly needs to tell Ron and Harry that in having the choice between a slow and painful death by the Lestrange brothers and life she choose life, and that she made this decision after being captured and tortured for a while with no signs of rescue from the Order. If people begrudge her that, she might thinks twice about the value of their friendship. B) Hermione's mum might have her very understandable initial skepticism but in the end Hermione's happiness, Yaxleys courteous behaviour and having lovely grandchildren will out weight that. C) And therefore it might be a good idea to lay low for quite a while, for instance in Canada, like Theo, or in Australia. D) see C E) I understand your concern but I do not share it. First of all, I think Hermione will view the war as the thing that robbed her from her youth and not Yaxley. Secondly, she is a very practical girl who doesn't dwell on things. She choose to live and she will live with the consequences. Thirdly, Yaxley might be in his seventies but as being a wizard he'll not look older than still being in his fifties, like Ro said in her diaries. And last but not least: she might be 23 in age but she won't feel like being the average 23 year old girl with all her experiences in the war. Yaxley is only a part of that. Even if she had not met him and went through the events in canon she would have been different from other 23 years old. F) I think knowing he loves her is more important to her that the actual marriage. What she doesn't want IMO is only being a sort of surrogate for his late wife without being loved. Knowing they love each other will make things more equal for her, even without a marriage. I think she is also in this kind of things a rather practical girl. G)I think this midlife crisis won't happen, just because of the fact she is both practical and someone to commit herself wholly to a cause. She will view the glass as half full and not as half empty. Apart from that, it's not an arrangement in which she is powerless, especially since he is in her custody after his trial. I think that kind of things work well on a psychological level for her sense of equality in a relationship. I also think she has all kind of possibilities to develop herself even if she might not be able to work. We have already seen Yaxley preferring to have an intelligent wife / mother for his children, so she would be able to do for instance some independent research.
I really like your idea of writing a sequel. By the way, I do have a LJ account with the same name so do feel free to PM me if you want to discuss this further.