If you’re a licensed gun owner and own the gun legally demand a jury trial. The Crown will tell you that you can’t have one but you can. They have no hope of empanelling a jury that will convict someone for returning fire while they are under fire as long as they are licensed and own the gun legally.
You shouldn’t be returning fire without confirming your target and what is beyond it in that situation. Of course many people will end up following instincts first and think later, especially in dangerous situations. The best option would be having an escape route, or multiple, and if you’re paranoid or a likely target, practice using them often. Returning fire should be a no other reasonable options route.