If one is declared and you do not evacuate, the 911/emergency cannot and will not respond to any requests. You are on your own.
In practice, is that what actually happens? (And do people believe that is what happens?) Many requests for help have paths other than / in addition to 911. It’s hard to believe a responder able to respond to a serious or life threatening situation nearby would not. Granted that if responders are overwhelmed, there might not be any responders near “mandatory” zones in early stages of the rescue efforts.