Can you take an electrical supply off a fire alarm panel to a gas shutoff valve and if there was a fault on the fire alarm panel would it give a signal back to the shutoff valve to close?

In general, any device powered by the fire alarm panel must be listed as compatible with it. There are probably few, if any gas shutoff valves so listed, so probably not.

The normal arrangement for this function is to use auxiliary contacts, either on the panel itself or an intelligent control module to switch an external power supply. This connection should be wired "fail safe" meaning the valve would close if the external power failed.

If you asked this question, you are probably not qualified to design fire alarm systems. This is a life safety system! Get a qualified engineer or NICET IV designer to make sure you have it right. There are numerous codes, standards, and local amendments that must be followed, as well as the manufacturer's guidelines.