HW, I should imagine there will be a huge amount of relief once your H leaves the company.
There's no point in berating yourself for the way you handled things when first happened.
I don't know all the details of course but tbh, I don't really see what the company could have done to "punish" her. Surely any disciplinary action would have to have been taken against both your H and the OW and only if there was a clear company policy on relationships amongst the staff.
Again I don't have all the info so forgive me if I speak out of turn but, IMO the company don't have any duty of care or responsibility to you. Only to their staff.
Ultimately, whether they handled it properly (legally or morally) they are going to end up losing a key member of staff.
The OW didn't get his job, she isn't happy with what she did get and I am 100% that the office rumour mill will be pinpointing just exactly why your H has decided to leave.
Ultimately, it's all so very very very close to having a line drawn underneath it.
New job, fresh start without OW constantly in the picture.
I admire you enormously for having the dignity to not cause a hellish scene and to support your H in his job under extremely hard circumstances.
You have retained your dignity and you should be proud of that. Don't let that pride be tarnished by bitterness towards H's employer.