An extension based on marriage does not need a 12 moonth history of funds, just 3 months to show the 400k has seasoned for 2 months prior to the application
If your husband gets new insurance and does a border bounce before the Non-OA expires (the visa not his entry stamp) he will get a new 12 month stamp but will require a re-entry permit to re-enter after the visa expires
It is highly likely that the financials were already in place for the Extension of Stay so there should be no issue starting again if his Immigration Office is not one which will not do the conversion