In that case our only option is to wait. We get safety checks every 30 minutes. If we don't respond Code-4 (we are ok) to the checks dispatch will start to send help.
We had a local fire and ambulance crew get caught in the middle of a gun fight not too long ago. Talking to other employees of that service I guess you could hear them asking for help and hear gun shots in the background.
If we can't talk, and are being held, I figure hold an open mic on the fire channel. Hopefully it's in PS or CC so they dispatch them right away since it's unified.