Before you die, you can indicate what you want Facebook to do with your account after your death. You can choose to have your account deleted or memorialized by setting a legacy contact. If you do not set a legacy contact before you die, Facebook will remove your account but they will need documentation from an immediate family member or the executor of your account before they will do it.
Facebook says the quickest way is to provide a scan or photo of a death certificate. Other items that will be accepted include: power of attorney, birth certificate, last will and testament, or an estate letter, and either an obituary or memorial card. You also have the option of asking that your loved one’s account be removed or memorialized.