http://www.businessinsider.com/gt-advanced-files-for-bankrup...
At some point the corporation decided it wouldn't outsource software development work anymore. They hired some of the key people at my former employer (by then I had already moved somewhere else), and almost overnight they had to close shop because they didn't have a source of revenue anymore.
Wise agencies try to diversify - but any new business brought in will have to deal with The Big Client being the squeakiest of wheels (... that get the grease).
I can't say I've see an agency that has made the "grow other business" transition successfully.
All you can do is hope that you can nail down the next large customer before your existing golden egg figures out they can push you around.
I've often wondered how well a restaurant would do in areas where those platforms are popular if it just dropped its customer-facing storefront entirely and went entirely online delivery.
The drop in operating costs versus the lack of walk-ins ...
I expect you'll see more non-traditional kitchen locations and alternative delivery transport methods (e.g. scooters or Postmates bike couriers) to combat the high rents, congestion and parking issues common to most dense cities.
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.