Personally I think it would be a little too convenient for Luke's hand/lightsaber to be falling down the same shaft he does, not to mention at about the same time even though there must've been at least a minute between it being cut off and Luke jumping.
And why would the hand still be holding on to the lightsaber, it's not impossible I suppose but certainly improbable.
I think it would be best if it was just a piece of the metal vane or something.