The breaking up of the OTP is in a way what started this ship for a lot of people when the first comics Civil War happened, so this isn't exactly surprising.

It sounds like you have an outline and plan here that is pretty progressed. I like the idea that this would be Natasha-centric and dealing with how everyone reacts and processes their loss. So the first part would be focused on how everyone is affected and show how Tony is coming to grips with his feelings?

It's good to have an idea where you want this to go. Have you started writing yet?