26
You disregard the hail with one quick press of a button on your comms unit. Coulson would be proud, you think; he's spent the past several years trying to teach you about things like 'radio silence' and 'communications security' and so on, and you're finally applying the knowledge.
You have about five minutes to enjoy the sensation of being pleased with yourself before you feel a cold sting at the back of your neck and you're falling. As the edges of your vision go red, you see a flash of movement in a tree not far off the edge of the roof behind you - sniper, damn, you should have seen that.
Maybe that's what the radio call was about.
Either way, with this kind of bleeding, you know you don't have long to regret not answering. Hopefully, the mission will succeed without you.