I mean, he'd probably still use his sword. I imagine him being like Robin, a magic user with sword attacks.
I've never played Golden Sun, but all I ever hear from people is that it looked pretty and had way too much dialogue.
Golden Sun had a lot of puzzles where you would use specific "psynergy" (the franchise's form of magic) to solve the puzzles and continue on with the game. Yeah, Isaac had a sword, but the sword is the least interesting thing about his moveset.