My thoughts are they should talk to Citizen's Advice, who will probably advise them to be up front with the lenders, especially mortgage lender, who will want to find a mutually acceptable way forward in preference to cutting losses and bringing it all down. It's more profitable for them to do so.
Having no insurance is a risk, but one can opt to take it. May get away with it, may not. That said the mortgage lender will probably have a rule about house/building insurance being obligatory since they won't want risks to be taken.