On superuser we tended to delete April fools day questions right after april fools day. We did it for two years (we forgot this year :/).
Last year we decided the questions had historic value, if nothing else for when its referenced on chat. I ended up creating a meta question, similar to the many memes of meta, and added a screenshot from firefox to the question
There should be no expectation of survival for a AFD gag, but really there's no reason it should be consigned to the dungheap of history.
