Still, since old EU is scrapped, it’s not difficult to imagine that saber fell into a random air chute…
Right. Then the vent opened up and the lightsaber fell out like Luke did and then fell to the core of the planet and melted.
I think the reason Luke fell is because he did his best to stop himself from letting himself slide through the whole tunnel. It seems apparent that if something is not moving through the tunnel as it should and just sits there, then it gets sent to its doom. That saber on the other hand (no pun intended) could easily slide on and on since it’s not trying to stop itself from going who no knows where. Surely the end of the tunnel doesn’t lead to the outside? I would imagine there’s something tangible for it to land and someone to retrieve it.
Of course, this is all speculation, but upon quickly watching that scene of Luke in the tunnel, he could had kept sliding through but instead intentionally created enough friction for him to stop.