I accidentally "disappeared" my first FB account by creating a new account and unwittingly using the same email address as the existing one.
No warning, nothing. But I could no longer sign into the first account.
When I realized what had happened, I went looking for signs of the that first account. I had been the sole admin of a group; now, that group listed no admin at all; I seized admin rights with my new account.
So perhaps that's the best way to deactivate: exploit bad code.