If “Parasite Paracide” is flipped and then destroyed as a result of battle, it does not go into the opponent’s deck.
Netrep Q&As:
Q: If a face up “Parasite Paracide” is drawn while the player has a full Monster field, what happens to the “Parasite Paracide”?
A: It is destroyed because there is no room on the field. bishop 02/23/2004