Okay, it has been brought up on the Wild Mass Guessing part, but it really belongs here: WHAT THE HELL HAPPENED THAT MAKES THAT DREYFUS IS BACK AFTER THE PINK PANTHER STRIKES AGAIN?
My theory was always that most of "Strikes Again" was some nightmare, or hallucination that Dreyfuss was having while locked up in the asylum.
Personally, I just assume that "Strikes Again" takes place after "Revenge", and the later films done after Sellers' death aren't valid at all, considering such details as Dreyfuss being in charge again.
I always assumed that the deathray's effects were only temporary, due to an (unintentional?) oversight on Fassbender's part. Presumably the UN building came back as well.