Not ony is this a single point of failure but it's one they've no control over whatsoever. Same goes for Google/Youtube etc. It's as risky as flying a passenger jet with only one engine.
What are they thinking, why are they prepared to risk everything?
It boggles my mind.
If you had a restaurant, would you source your produce from your trusty friend who grows vegetables as a hobby or from an established mega-farming-company?
The big advantages with the 2 person startup are
1. A small business a customer who matters to them, and you will get better service
2. You can get terms such as having control of backups, hosting of your choice, and access to systems so you can get someone else to maintain things
> Contracts come with strict terms of service, SLAs, service expectations and such.
How close do these come to covering the consequential losses of an extended outage?