If a company folds owing money under this scheme, then it seems clear that it (or the members where PGs have been given to the bank) are liable for the 25% not guaranteed by HMG.
But how does the 75% work in practice? Do the banks automatically call in the guarantee from the government for the 75%? Or do they first seek to recover from the company / PGs and then only from the government if they can't collect from the company? Obviously, if it's the latter, that could be a problem where PGs have been given.