Sith Emperor is immortal but he can use the force to mind control many of his servants. His Voices have force bond with him. So he can be safe in one part of the galaxy and still manipulate the Empire as he sees fit.
Revan and Jedi Exile should have known better. Revan was a Dark Lord and Jedi Exile trained under a Former Dark Lord.
I am probaly the biggest fanboy of Revan and Jedi Exile but I do think that Novel should have been better without Revan or Jedi Exile. And expanded the Roles of Canderous, Scourge and Darth Nyriss. Both of the crew of the Ebon Hawk could have be expanded and still have a good story.