I've worked at a few such companies, and they all work extra hard trying to diversify their revenue sources, for both customers and industry. If it's a startup, then such revenue dependence can mean the difference between being able to go IPO or not.
For the situation you describe for restaurants, they'd have to be vigilant about catering to multiple platform providers, and not neglecting their in-person customers (I've definitely seen a restaurant cater more to delivery rather than sit down, and slowly deteriorating in reputation among customers as order times became longer).
It's just like managing an AAPL supplier contract. Some will thrive, and others will suffer, like the sapphire supplier in Arizona.