I adore this moment because Jyn’s first instinct is to fire back “well, screw you too!”–then she’s completely thrown by the fact that Cassian is actually there to support her.
If they had survived, Baze Malbus would have returned to Jedha after the war to rebuild the Holy City and would have found that the rains of his childhood still fell and that life always found a way back.
If they had survived, K2SO would have chosen to mentally simulate a scenario where Cassian Andor at last found peace and happiness, only to see it slowly unfold in real life as the war ended and the years rolled by. And both the simulation–and the reality–pleased him.
If they had survived, Luke Skywalker would have given Chirrut Imwe the Kyber crystal from his father’s lightsaber to set as the first stone in the rebuilt Temple of the Whills in Jedha City.
If they had survived, Bodhi Rook would have had a chance to save his family–not the one he lost on Jedha, but the one he found on a U-wing streaking through the broken sky as his city crumbled under emerald light.
If they had survived, Cassian Andor, who knew what it meant to take a life, would have lived to hold his own child in his arms and learned what it meant to make a life.
If they had survived, Jyn Erso would have looked up to find the horizon endless, would have seen before her brothers–big and small–that she had never had before, would have found that in the eyes of someone who loved her that her scars made her more beautiful, and that the aches in her body that never went away were not unkind because they reminded her of all the battles won and the people lost, all in the name of a cause worth dying for.
(For more of my depressing head canons, look here and here.)