If you delete your Facebook account, you won't be able to log into your Top Eleven account. As a friendly suggestion, if you are set on deleting your Facebook account, you can link your profile to your Google play or Game Center, so that you are able to log in into your account afterwards.

In order to link your account with another platform, go to Settings (the button in the bottom left corner of your screen), and press the "Connect" button next to the chosen platform.