Maybe she leaves to Coruscant after the battle. Maybe she’s requested for an emergency session of the Imperial Senate where some good old Emperor decides that due to the Empire being attacked it is about time to dissolve the Congress. Maybe.
The Emperor dissolved the Senate before the attack on the Death Star.
But that’s just what I would have done to solve the continuity issue. Perhaps they just do not care.
This. You are probably correct.
Mon Mothma’s been a founding member of the Rebel Alliance for as long as there’s been an expanded universe.
True. Thankfully, Disney expunged the expanded universe, so they still need a logical explanation for the inclusion of Mon Mothma in this timeline. And by “need” I mean they need a logical explanation so that the story makes sense, if they care about that at all anymore.
Please try to remember it’s a Rebel Alliance. It’s made up of a lot of different cells across the galaxy. Mothma was probably running a different division before they were all united in ROTJ.
This is not correct. In the original 1977 movie, the Empire is very clearly obsessed with finding the hidden Rebel base. Base. Singular. Not bases. See here: “This will be a day long remembered. It has seen the end of Kenobi, it will soon see the end of the Rebellion.” - Darth Vader.
Unless, that is, there were other Rebel bases that Vader and the rest of the Empire were not aware of…and that existed despite not being mentioned in the original movies or scripts.