The principle being "if we make life unbearable they will somehow find a way to leave, we don't care how as it's not our problem, and we don't care if it's so unbearable that the quality of life is significantly worse than the minimum our human rights principles theoretically guarantee".
Essentially, they are already supposed to survive on magic or starve and die, even though no minister would admit that. (And some of them _are_ dying.)
It seems clear that the government which instituted those laws does not seriously consider the wellbeing of that minority, as if they aren't people at all. Political statements like "making a country for the good of all" are meant to gloss over the fact that said minority is not part of the "all".
I think it's this principle which is in play on an ongoing basis, not the laws of the day.
So in a cashless economy, I think the principle of "as harsh as possible and we don't care about their wellbeing or basic human rights" will continue, and due to system side effects (rather than intentionally), the consequences will become progressively more severe for a minority.
For people to not be excluded in a near-future cashless economy, the driving principle would have to actively change, to make sure everyone has some access to the cashless economy, and at the moment, I see no sign that popular governments would implement something like that.
The unbanked, on the other hand, will be at greater risk of starvation when you need a bank account to obtain food.
Everyone can get a basic bank account, you say?
Well, it's the law in the UK already that some people are not allowed a bank account (you need to prove your right to a bank account in the UK, along with your right to rent shelter).
They are still people, and they will still starve in a cashless economy.
I know this, because I already know people who are getting by on half a meal a day, and that's today.