There should 100% be a system like the old season ticket cash top up available. Personally, I will probably look into those travel credit card things and see if there is a way to top up a card with what I can afford for spend at the Amex should the cashless system come in.
This is the case with most contactless transactions on most systems. However, once the connection goes down you cannot make any further transactions on most systems. The card machines will go down at some point, guaranteed, it does not happen often but it will happen one day.
This, I am not hard up by any stretch but I use cash 100% of the time as a way to budget. I withdraw a bit less money than I can afford to spend each month, once it is gone it is gone. No more beers, or extravagant purchases after that.