Do you have children or are you planning to? If you are, I can tell you that it can be really hard on kids not seeing one parent for extended lengths of time. It can be hard on a marriage, too. If you have already been through three years of that, you probably already know.
The brutal part of winters isn't the snow, it's the temperatures and windchill. The plus side is that it's more of a dry cold, so it isn't as bad as it could be. The whole state is very rural, but around Bismarck you wouldn't be as isolated. Folks here tend to be very laid back, and until the oil started bringing in people crime was very low (a murder anywhere in the state made front page news). Still not too bad, but it's on the rise.
I grew up in PA, joined the military, and my last base before ND was Guam. I was sent from the 'tropics to the arctic' and to be honest, I love it here. I hate the long winters, but really appreciate spring! There are a lot of military folks who retire and stay here.
If DH takes the job, why don't you come visit and see what you think? Then you have something to go on to help with your decision...