Look, you are asking a hypothetical question. Every electrical circuit will get fried. All electronic control units will be burnt out, all navigation and instrumentation will probably be worthless. What exactly more do you want to know? Why passenger aeroplanes aren't shielded with hundreds of kilos of lead each? I think Airbus and Boeing have quite reasonably taken the view that you can only defend an aeroplane from direct attack in this manner to a limited degree.