In my opinion, I wouldn't comp that much especially for the fact they lost nothing to me. It sounds just like a person who lost a diving suit and mk1 asking for a 600k comp. It's a bit unreasonable so you can practically just comp them a reasonable amount like 150k and make sure you have evidence that you gave respectable comp towards someone.
As long as you didn't hit the heli and all he did was hover instead of leave, then you're fine to shoot him out of the sky. This is reinforced by the rule here -
If a person does not fly away after given warning shots, you may then open fire on them.