Zebbi I don't like the idea of using pathfinding. With pathfinding the sword will eventually get stuck somewhere.
If this was my game, I would probably do this:
Launch the sword using Bullet behavior with deceleration and maybe small gravity. While flying forward, it bounces off walls and other obstacles, kills enemies. When it's flying back, it flies through obstacles. You can set its opacity to 50 or add some other visual effect to make it look like a "ghost" sword on the way back