When the cat whose account you run on this site disappears or is otherwise no longer with you, you have some options here.
From your User » Edit page, you can update your kitty's Rainbow Bridge status at the bottom.
If you have another cat, you can transfer your account to that cat's name and update your profile picture. All of the previous posts will show as having been made by the new cat.
You can also request that your account be memorialized and start over with a new account using your existing email address. In that case, I can change email address from this end, freeing the previous one for a new account.