Palpatine could only be resurrected on Exegol.
Palpatine was obsessed with eternal life before he even founded the Empire, only killing his master Darth Plagueis the Wise when he had learned the secret of essence transfer from him. The fundamental problem with essence transfer, though, lay in the Emperor's desire to find a suitable host for his dark side spirit; no doubt that was one reason he initially focused on Anakin Skywalker, believing the Chosen One would make the perfect host. In the end, he chose to possess a clone of his own body instead - but those experiments didn't go particularly well.
Star Wars: The Bad Batch episode 3 appears to have shown the beginning of the clone experiments that would ultimately lead to the creation of Palpatine's clones. The Kaminoan clone army was initially based on Jango Fett, but the genetic samples were degrading as time ed. With the Empire turning against the clone program, the Kaminoans believe they need to find a way to create superior clones. It seems likely they are attempting to create Force-sensitive clones - and indeed Omega may well be the first of these.
The future of this program is unclear, but it looks as though the Empire is destined to take control of the project. symbol was based on the Kaminoans. He was revealed to be an Imperial clone engineer, presumably working to create so-called "strandcasts" - genetically-engineered beings who can even be Force-sensitive. No doubt the Emperor himself prioritized attempting to prolong his life using the dark side, but Charles Soule's Darth Vader comics run confirmed he was interested in cloning as well. Palpatine sponsored a cloner named Cylo who created a personality map allowing his consciousness to jump into clone bodies, and this seems to directly foreshadow Palpatine's use of essence transfer to jump to a similar clone.
Star Wars: The Bad Batch has just hinted at the beginning of the Emperor's clone experiments - and we already know how they're going to end, in Star Wars: The Rise of Skywalker. It's going to be fascinating to see how the Kaminoans begin to develop the ability to clone Force-sensitives, setting the scene for a dark future.
