The feral cat idea would work... it really doesn't make sense that leopards would show up out of nowhere.
I have an idea for the sacrifice idea. How about the time limit the leopards/feral cats give the clans is running out of time and Wildifre (meh amazing Riverclan deputy) offers himself up as the sacrifice. He's brave and slightly stupid like that. He would do anything to keep his clan (and Ravenstar) safe so it's in his character. He could reach the leopards/feral cats and at the last minute attack them. He could be brutally injured but somehow escapes. What do you think about that idea? Tell me if you think it's stupid, I understand.
And you are important Feather. You're the head admin... what could be more important than having one of those? (Raven would say a cookie... ignore her)
OH OH ME ME ME ME ME ME ME ME ME ME ME ME!!!!!!!!!!!!!!!!!!!!!!!! Oh maybe Feather, since she's actually a medicine cat. No, you should send it to..... Darkfang!