My take is
Scemma is over, lets keep that and ignore the rest. Now with Hickman we get a new start, and Rosenberg's run will largely be ignored.
It's basically the same thing that happened with Bendis and Hickman when Hickman was doing Time Runs Out and Secret Wars, nobody ever knows what happened with the Nation X of Cyclops guarded by Sentinels Hickman created because it was ignored completely. I doubt Hickman will have a hard time ignoring the terrible books of these last years.
BTW, I think Emma in black, being the hellfire king, and the character assasination of Shaw (even villains can be character assasinated), were all bad things. So i don't have a problem with that stuff getting retconned out or ignored.