[aeronaut]

My educated guess would be no. The general guideline for playing cards is that card effects are resolved in the order played, so once the Potion of Cowardice is played, the PCs are running away, whether the monster is out to lunch or not. Conversely, if the "Out to Lunch" card were played first, and there were no other monsters, the potion of cowardice could not be used, as there were no monsters to run away from.

In general, for a card to supercede another card that has already been played, the new card must have text that specifically allows it to affect the card already played.

aeronaut