If you have a cell phone 911 should work whether or not you have service.
You'd still have to have a cell signal. It appears that the city's approach was, probably necessarily, ham-handed in that they simply shut off the equipment. They have no access to the actual carrier's multiplexing equipment where they could in a more elegant manner turn off the exact services they wanted to. Hence the 911 interruption. I doubt if this is over...a significant test case may come from it.
No, they turned off the power to the radio equipment which makes any call possible. So they turned off the 911 service as well as any other service - including text messages, etc.
Stupid move if you ask me, because it endangers anyone who might have needed to receive a call or make a call, even a call for help.
And of course telling the world about it is even more stupid. Now any criminal or terrorist knows that you can turn off the ability for people to call 911 from a BART station by just turning off the power to a local cell which covers the station.
The idea of turning off communications, including that used by innocent people to get help in an emergency, just because it might reduce the ability of trouble makers to organize is a really bad idea.