The lightsaber was recovered by a maintenance droid from the shaft and then almost smelted by the droid's supervisor. Vader showed up instead and got the lightsaber back. I mean, it was his lightsaber. Palpatine took the lightsaber (and the hand holding it) as trophies, eventually creating a clone of Luke from his severed hand, and arming the clone with the lightsaber. Then some **** happens, Luke gets it back, and gives it to Mara Jade, his love interest.