Right, you seriously want giffgaf to send a text to say that texts were no0t working? Or was this supposed to be a joke?
Even when the network is working normally, giffgaff has to schedule bulk notification texts over 3 days (like with the clock change announcement) so the messages would be obsolete by the time they are delivered. And in the case of the text service itself being down, even the first of the messages would not arrive until after the service had been fixed.
There's already a place where you can find out whether there are known problems whether they're local or nationwide -- https://giffgaff.com/coverage-and-service#network -- and by 9am it had a banner at the top so you didn't even have to enter a postcode. There was also a prominent banner on the giffgaff login page.
There's also a service updates forum https://community.giffgaff.com/t5/Service-Updates/bd-p/Notice_board and a thread there which announced the problem at 7:05 am.
The facilities are already there -- perhaps more people need to know about them, but they are there.