THis is a dumb question, but after the final main story mission can you free roam the galaxy and finish undone side quests? I hope I explained this well enough. THank you in advance.
No. After you finish the main storyline, the game ends. And I'm pretty sure that somewhere near the end of the main storyline there's a sort of cutoff-point where you can't finish side-quests as, without spoiling anything, I just don't see how you could after a certain point.
After beating the game you can however restart a new game with the same character, and you get to keep your weapons/armor/items, your levels, and I believe you also get to redistribute all of your skill points you accumulated in the last game.