Where did the cats go update

 It's just occured to me that there a third possibility for the missing cats.
 Douglas Adams book the Hitch Hikers guide to the Galaxy had the dolphins leave earth just before the Vogons destroyed it (from memory I think it was actually the book called so long and thanks for the fish that explained why)  So maybe the cats have all left before earth gets destroyed by the Vogons  We can just hope so......