Tiberius
Explorer
I concur. XP is awarded for defeating a particular encounter. While typically defeating is parsed to mean "killing in combat", it is possible to defeat an encounter through diplomacy or simply circumventing it. This being the case, your PCs did not defeat the encounter, they were defeated by it. Therefore, I would award no XP for the PCs, but would award it to any guards who survived or were subsequently raised.
-Tiberius
-Tiberius