Rizzen's head can be taken from his corpse, if the Princess decides to follow trough with Sioril's proposal to show her a way to the Moonville Castle in exchange for killing Rizzen during her Moonville adventures.
Alternatively, it is the severed head of another drow, which Rizzen carries in his backpack and which remotely resembles Rizzen's, after he has worked on it. According to Rizzen he took the head from one of his sister's consorts, after the last battle fought in Maeralssin. It can be used by the Princess to fool Sioril and make him believe she has killed Rizzen for real.
Conundrum
- Shouldn't a severed head of dead drow stink like hell?