UPDATE: I had a chat with the guys running this question, and here was their response:

the short answer to that question is, thus far, and as far as we can tell, the shop owners cash out until they've satisfied themselves that Bitcoin is real money, they do this via platforms like Paxfull and Bitrefill, if they haven't got bank accounts. But once they're satisfied that it's real money, they tend to hodl, it seems like, for the most part, they see this as an investment opportunity the likes of which they've never really had before.

Admittedly this is OK, as long as the Bitcoin being spent at their shops represent a small part of the turnover, which it does, for now. The only people spending Bitcoin in the township is our coaches, and some of the older kids. If it grows, we will have to find other ways for them liquidate more easily, unless off course by that time, larger stores accept it and they can buy stock using Bitcoin. That would be the ideal scenario.