A better way of looking at this is…
Don’t rely on Blynk or ANY IoT system for your mission critical control.
If your device setup controls a local detection, alarm and extinguishing system, then it needs to fully and timely function, regardless if there is an Internet connection and/or Blynk Server connection. This can easily be done in your code… here is one example of a way to keep your system running without a Blynk server link.
Other than that, Blynk is a perfectly good system to use for passing on the monitoring status and alerts to a remote local.