Just read a YouTube comment about how bringing people back from death(like Ventress and Rey were resurrected) in Star Wars is easier than preventing it.
Well Sidious did say the power to cheat death is a power that only one has achieved. He was unaware of Momin until he got his Helmet.
On top of that he tried to open a time gate… I would assume Plagueis was the one who provided Sidious that time gate.
Anakin upon becoming a Force Ghost was able to move Ahsoka to the World Between Worlds while having it be on the border to reality enough for people to hear their duel before returning her to the Galaxy without throwing her through a Time Gate.
Plagueis was just as powerful it would seem. Strong enough to be able to go to any point in time as well as any location without a Time Gate and save those he cared about from dying and grabbed all the Sith’s Souls right before he died and failed an attempt to possess Sidious(after Sidious killed him in his sleep) getting consumed by him.
Sidious clearly wasn’t smart enough to learn from the Souls and just received their raw power though it seems he did preform Plagueis’s Force Possession technique and found his new Body starting to rot and mused that Plagueis may have been having the final laugh on him.
The Chosen One destroyed the Sith in terms of body and then brought Ultimate Balance to the Force sending Ahsoka to Peridia where a Dark Side Power lies hidden.
Of course since Sidious mused that his rotting state may have been from Plagueis having the final laugh on him(understandable as absorbing Rey and Ben’s Dyad healed him rather than accelerate his demise) and admired Plagueis for being a prophet it may be that Plagueis rotted Sidious then waited for the dyad to show up to devour it’s power then allowed Sidious to die at Rey’s hands before heading off somewhere like the Sith Emperor!
Of course that’s assuming the one rotting Sidious from within isn’t the Sith Emperor himself…
Would love to have Vitiate appear gloating about having allowed himself and the other Sith to be consumed by a Time Traveling Plagueis so that he could claim the Sith’s combined power only to learn of the Dyad from reading Plagueis’s mind and thus orchestrated Plagueis and Sidious’s demises in order to become the Final Boss for Anakin(who attained Inner Balance) to defeat to bring Ultimate Balance to the Force.
The Chosen One Prophecy according to the Qui-Gon Novel is thus:
Only through sacrifice of many Jedi will the Order cleanse the sin done to the nameless.
The danger of the past is not past, but sleeps in an egg. When the egg cracks, it will threaten the galaxy entire.
When the Force itself sickens, past and future must split and combine.
A Chosen One shall come, born of no father, and through him will ultimate balance in the Force be restored.
The first of the lines I highlighted may reference the Sith but the second one seems to reference Time Travel… Past and Future splitting and combining… I hope that means we will see Valkorion or Plagueis(empowered by Sidious’s demise after eating him from within) and Sloane become a threat.
