What happens then? Well, the Emperor speaks to you. His actual physical body may be more or less a rotting corpse, but he's still conscious to some degree and that close to the Throne he can manipulate reality pretty freely. So he can still talk, either out loud or directly in your head.
Actualy, im pretty sure that the huge leadership issue's the imperium has is largely a result of the emperor not being able to do any leading anymore, and that he cant talk at all.

Though of course there is allways a few crazy people claiming that the emperor has spoken to them.