...this is followed by a try of server migrate, that results in game hung / black screen.
There are several issues here:
Server crash that should not happen.
Unsuccessful server migrate operation. I doubt that server could migrate to exact same state, but at least to last checkpoint should be possible.
Game hung / black screen upon unsuccessful server migrate operation.
In case of server crash player / party is migrated to new dedicated server and start from last checkpoint with the setup (guns, ammo, items) they had when checkpoint was created.
Player / party returns to lobby / main menu and is able to cleanly exit a game or queue for a new match.
I observed this issue serveral times since game was released, always in the same area (Chaper 2 'hold off metro area' in New York episode)
Currently when it happens, I need to forcefully exit the game by pressing Alt + F4.