I think your husband is going through what many of us go through as we get older - that indefinable need to return where we belong. My yearning started a few years before I hit 50 but now over 60 the pain is getting worse and I am stuck here - trapped in a time warp.
I think there is so much more for kids to do in UK, far better opportunities being in the big European pond rather than a little Aussie one. If you feel that you can live there then go for it - he is just about as old as he would want to be to resettle - any older and it could be a bit more of a challenge but there are a load of 50s and 60s returnees (on another board) who are finding that it is working really well.
There is no guarantee that once they have left home the kids would want to stay in Australia (one of mine hasnt!) then where would you be? Stuck in a place because of the "kids" with no kids around you anyway. You have to live your lives for yourselves.