I'm not saying this is the same thing, but I had a terrible time with asthma as a kid, I was always being rushed off to the hospital, supposedly the ambulance guys even knew me by name. In the summer time I couldn't walk 50' without having an attack. And as far as allergies goes......well there wasn't much I wasn't allergic to! Between spring, summer and fall I had zero relief....I always was slobbering and rubbing the crap out of my eyes. My point is, "I never died", frankly I've never heard of anyone dying from asthma and allergies and Lord knows those conditions certainly didn't slow me down any.
Good luck with your decision............oh, one last point. Out of the six reasons you've mentioned, IMO no. 4 is the only worth while reason I can see you have for staying when considering the health of your children......sometimes family makes all the difference. Again IMO your other points are coloured with selfishness.
Again, good luck with that decision Greg. I wish the children all the best.