Q: Is rennet from a dead animal (not slaughtered) permissible to consume?
A: Milk from a dead animal (not slaughtered) is impure because it is a liquid that has come in contact with an impure vessel and thus becomes impure. Rennet from a dead animal which is a yellowish substance that is extracted from the stomach of an animal and processed to make cheese is also impure as is the skin-lining of the rennet.
This is the position of the school.
However, it has been reported that it (the rennet) is pure and permissible.
Source: Kashshaf al-Qina', Sharh al-Muntaha, al-Insaf