Caporegime
If you have zero chance of paying off the loan it means you are earning under £21k a year and so aren't paying anything anyway. You only start paying for it after that threshold. It is sort of like a graduate tax but you don't have unlimited liability...
No, ministers have admitted that half of all graduates will not pay back the loan in its entirety. This is why the proposals simply do not add up and once adopted will almost certainly change so that students have to pay even more.
With a graduate tax you have zero debt, under these proposals someone doing a degree in Medicine could end up with a debt of £70k from tuition fees alone (Source)