EWTN Catholic Q&A
Question from Christina H. Myers on 04-02-2005:

I believe someday he will be declared Saint Pope John Paul II the Great. Many saint's bodies have been uncorrupted by death. Will our beloved pope be embalmed before burial?

Answer by David Gregson on 04-03-2005:

The Holy Father has not been embalmed. My understanding is that his body was injected by a preservative fluid, but that his organs remain intact.

However, we cannot presume that, because a person lived a saintly life, he/she will necessarily remain uncorrupt after death. The bodies of many, probably most Saints have returned to dust and ashes. Incorruption is a sign of sanctity, but not a necessary sign, and is not taken account of in the cause for canonization.