[Retros] DR vs forced ep: what rule predominates?

[Joost de Heer]

Theoretically one could have the following situation: An en passant 
capture needs to be validated by an AP move, but this AP move is 
impossible because the position after the ep move is dead. Would that mean 
that the ep move is illegal, because its legality can't be proven, even 
with AP logic?

Practically, I doubt such a position exists.

Joost