I’m always circumspect when dealing with anything that comes from anonymous sources, so I’ll note that here.
But I do know that Donald Trump is in a bit of a pickle where this whole thing is concerned for one simple reason: It’s much more difficult to deal with a Rod Rosenstein departure if it comes about via firing instead of a resignation. If Rosenstein resigns, then Trump can appoint an acting replacement to serve indefinitely without having to deal with any sort of confirmation process. If Trump fires Rosenstein, he has a much more difficult process to go through – and that gets tricky since any Rosenstein replacement also inherits oversight of the Mueller investigation.