So he had an interest-only mortgage and an under-performing endowment that did not pay it off?
Presumably because it's all been throught the courts, any misselling compensation has already been dealt with too, but there is still the £43k shortfall.
Yes it does sounded as if he would have been better off with a repayment mortgage, but the warning letters about underperforming endowments have been seriously clear for the last decade or s,o in order to give people time to plan how to pay off the debt at term. That you pay 2-3 times original loan over life of mortgage is typical, so i wouldn't expect grounds for complaint there.
The angle here that I'm less sure about is his illness, as of course that might mean he cannot remortgage as he is now pretty much uninsurable. What a mess.