Along with executing the Grand Plan of the Sith Order and wiping out the Jedi from the
galaxy, discovering the secret to immortality was among Darth Plagueis’ greatest ambitions
during his lifetime, one that became a near crippling obsession during his final years.
Palpatine was fully aware of his Master’s experiments of the force and desire to achieve
immortality, once being quite amazed himself of its progress after witnessing Plagueis
resurrect a sentient being through the force alone.
So why did Palpatine throw away his one chance of immortality by killing Plagueis before
allowing his Master to make the breakthrough and having it later be taught to him first?
Well there’s one main answer to that.
Palpatine’s greatest and unmatched desire in the entire galaxy was to rule everything
with absolute authority, and the one thing he could not stand was to share that power
with anyone, including even his Sith Master
Plagueis’ initial plan for ruling the galaxy with his apprentice involved having Palpatine
act as the public figurehead of their future Sith Empire, while behind the scenes Plagueis
would be the one who’d call most of the shots.
He didn’t particularly care that much for fame, and was far more interested in forging
the galaxy in his own vision as well as experimenting with the dark side to its fullest extent.
Plus having a cunning Human, like Palpatine, would have made ruling the galaxy far easier,
especially in a political environment that was dominated by Humans.
But this plan of action was of course completely unacceptable to Palpatine.
He wanted it all, and he was even willing to give up immorality just so he could bask
in unlimited power all to himself once he achieved the Sith Grand Plan all on his own.
So he went through with killing Plagueis the very first moment he was vulnerable, during
his first deep slumber in countless years.
Palpatine had planned on killing his Master for years at that point, but never had the
safe opportunity to do so.
And it was likely he wanted to do it before Plagueis learned the secret to immortality,
as how does one kill a being that can just resurrect themselves from death?
Had Plagueis learned how to bring himself back from death through the force, it would
have been nearly impossible for Palpatine to get rid of him, or at the very least extremely
difficult and super risky, as he’d never truly know if he had killed him for good or
if his Master would one day return and strike back when he had his guard down.
Actually, when Palpatine successfully ended his Master’s life, he felt a disturbance
in the force right afterwards.
For a split second he actually feared that Plagueis may have had already achieved immortality
and kept that knowledge from him, but he later dismissed this concern after learning that
the disturbance likely came from the defeat of his apprentice Darth Maul, which happened
at the exact same time as Plagueis’ death.
While all the knowledge and progress that Plagueis achieved into trying to attain immortality
through the force died with him, it didn’t stop Palpatine from attempting to accomplish
that same task once he became Emperor.
But he never got close, instead having to settle with the ancient Sith ability known
as Essence Transfer.
While this ability allowed Palpatine to return back to life in clone bodies by transferring
his spirit into them, it wasn’t a sustainable means of immortality, as the clone bodies
degenerated rather quickly due to extreme dark side corruption.
This forced Palpatine to continually ditch his withered clone bodies and transfer his
consciousness into a new body over and over again, up until his final death when his spirit
was trapped mid transfer by a Jedi knight that sacrificed himself to contain the Sith
Lord’s spirit.
And with that Palpatine lost on that gamble in ruling forever with unlimited power, for
had he remained loyal to Plagueis, it’s very likely he would have had access to true
immortality and been allowed to remain a powerful figure in the galaxy, despite being a puppet
ruler to his former master’s vision of the galaxy.