If it's a localised problem i.e. malfunctioning terminal, they lose. Customers likely to go elsewhere. Like others I've watched what occurs. It usually applies in the bigger towns in the case of where there are multiple outlets e.g. cafes and the like. If it is on a wider scale, it depends for how long the outage is.
Beyond a day many customers get twitchy especially those who already have limited funds and are stretched to pay the bills. A number go off the deep end the moment it happens as the electricity bill is due, pay hasn't gone in (which can occur due to other reasons beyond eftpos failure) and they have little in the bank anyway in order to fund a direct debit.
Overall I think it is businesses which have the most to lose and that isn't good given the higher failure rate for small enterprises. May tip them over the edge. Sure there will be a few mutterings of outrage on the preferred social media sites at what has happened to their favourite but they majority stay silent and find a similar business in some other location. In twelve months or even less the failed business is mostly forgotten. Meanwhile, the landlord of the commercial premises goes looking for another tenant to shake out the welcome mat.
I find that truer of larger businesses, such as mine. I could change to a cash only system, but I would have to downsize and let some staff go.
Smaller businesses are more suited to cash only, I know of a few that are having no issues running a successful business with only cash. They seem less stressed. They also use going to the bank as a time to visit the locals and get in some networking.
In the suburb that I operate my business is a small family run fruit and vegetable store, they only open on weekends and only accept cash. they have run their business like that for the past 20 years, and I have never seen a shortage of customers.
Then there's the lovely lady and her daughter that live in my home suburb that make specialty cakes for birthdays, weddings, and so on. Cash only, and they have been operating for 10 years. All word of mouth.
My mate's wife is a hairdresser, she has a lot of older clientele and does a lot of home visits and does not have a mobile eftpos. Her customers pay with cash and have done so for nearly 20 years.
I have to contend with issues with eftpos that has been increasing over the past several months. I am with a large bank, I have the latest and greatest eftpos tools, I have back up internet with two different providers. And still, I have a weekly issue which causes me to waste my time and my customers time, it can be stressful.
Cash is not stressful. And if you have a product or service that people want and like, they will pay for it any way that the provider wants. Cash is easy, for those that know how to use it