Sure they may end up doing it that way, although I agree it would not be the best solution. As I said, it would limit the amount of players available to join. I am sure they would prefer to find alternative solutions.
I certainly agree there needs to be a change to the way it currently works. I would certainly submit this as a bug to Zendesk to make them aware of this being an issue. This issue is however quite different from moving galaxy through ‘normal’ gameplay, as that would indeed remove your base and all data associated with the previous galaxy. All this data actually gets deleted from your save. (or at least used to)
They can’t just do the same when joining a player in another galaxy, as you are a visitor. This means that if you continue with your own game without joining, you will be back in the galaxy you are actually in. Any base you created by joining another player in a different galaxy, can only be continued with by joining a player in said galaxy again. At least this is how I understood it to work, but not actually tested myself as I avoid multiplayer for now. So I believe that your a) is actually already the case.
Speaking of b), I don’t see that happen either, as it doesn’t make sense for the game. It would result in unlimited travel across the universe, making it way too easy. Not to mention it requires pretty much the same solution as I suggested, since it would then require saving galaxy together with the coordinates. So for that matter they may as well lock locations in other galaxies, instead of allowing them, since the logic is saved already.
Whichever they decide on doing, I think we both agree a change is required. I am mostly amazed about the fact they did not think this through … what else is new though … Take it up a notch HG, please!