É uma chamada do DM
As regras 5e não tratam disso, então é uma chamada do DM. Se um DM está procurando precedência histórica de edições anteriores para ajudar a orientar sua decisão, o 3.5e tinha a seguinte regra para formulários alternativos (que incluía Wild Shape ):
A creature using alternate form reverts to its natural form when killed, but separated body parts retain their shape.
... enquanto Alter Self (que incluía Polymorph ) tinha a seguinte regra:
When you revert to your true form, any objects previously melded into the new form reappear in the same location on your body they previously occupied and are once again functional. Any new items you wore in the assumed form and can’t wear in your normal form fall off and land at your feet; any that you could wear in either form or carry in a body part common to both forms at the time of reversion are still held in the same way. Any part of the body or piece of equipment that is separated from the whole reverts to its true form.
Isto implicaria que você teria destacado cabelo humano (e um careca Sorcerer) quando o polimorfo terminasse.