Check for positive signs of fire - if you only rely on the firewire then you do risk panicking for no reason. If you have mirrors, use them - if you have a crewman get him to check - if not put in a turn and look behind you for smoke.
I have seen the effect of a fuel line fire in a Lynx and it burns so fiercely that the aluminium of the airframe starts to melt - now if you want to climb to 500' and sort it out well fine but I would be looking for a quick circuit back to the rig in case it doesn't go out when I pull the T handle or-worst case setting up for a ditching.