Praise be to Allaah.
The thief has no right to have the amputated hand reattached, because that means that the signs of the punishment for his crime disappear, and the effectiveness of the rebuke and lesson is lost. It is contrary to the idea of punishment and example as mentioned in the verse in which Allaah says (interpretation of the meaning):
“And (as for) the male thief and the female thief, cut off (from the wrist joint) their (right) hands as a recompense for that which they committed, a punishment by way of example from Allaah. And Allaah is All‑Powerful, All‑Wise”