The Star Wars saga concluded in Star Wars: The Rise of Skywalker with Palpatine’s final death, but the legendary Sith Lord could have survived yet again. In the final installment of both the sequel trilogy and the Skywalker Saga, Palpatine is revealed to have not only come back from the dead since Return of the Jedi but is also the mastermind behind the First Order and its original Supreme Leader, Snoke. The Rise of Skywalker appears to be heavily inspired by Dark Empire, a comic series from the original Star Wars timeline, Legends (formerly called the Expanded Universe prior to the new sequel trilogy). Palpatine’s resurrection is similar in both properties, though the film offers a possibility of him returning yet again to menace the galaxy.
In Dark Empire, Palpatine is revealed to have transferred his consciousness into one of many cloned bodies he kept in his secret fortress world of Byss. The Deep Core world also housed a backup portion of the Imperial Military, complete with advanced units and new superweapons. This hidden faction was called the Dark Empire. In general, The Rise of Skywalker follows the Legends-era story quite closely, with Palpatine’s clone bodies and hidden military forces being stores on the Unknown Regions world of Exegol. In both versions, Palpatine proved he learned a method of immortality from his late master, Darth Plagueis, which was used to explain his shock return in the comics and ROS.
Palpatine died multiple times in Dark Empire, each time transferring his essence into yet another clone body. Palpatine only truly died in Dark Empire III: Empire's End, when his spirit was trapped in the Force by Empatojayos Brand and the ghosts of all deceased Jedi. In The Rise of Skywalker, Palpatine has only come back from the dead once and perishes again when his granddaughter, Rey, reflects his own Force lightning at him, disintegrating the emperor and destroying much of his fortress. While this appears to be his ultimate defeat, it doesn’t seem impossible for him to survive once more using the same method as before.
Unlike in comic series Dark Empire, Palpatine’s soul isn’t trapped in the Force at the end of The Rise of Skywalker. Palpatine is disintegrated by his dark power, but his death on Exegol seems similar to his previous demise in Return of the Jedi. The Sith Eternal cultists and Final Order military forces appear to have been wiped out on Sith planet Exegol as well, but if survivors were to clone new bodies for Palpatine on another world strong with the dark side (such as Moraband or Mustafar), the spirit of Darth Sidious could return once more.
From a real-world perspective, Palpatine is one of the most iconic villains in the Star Wars franchise. Bringing The Emperor back for the final sequel trilogy film (and retroactively making him the mastermind behind the First Order) was, among other things, a way to tie all nine saga films together. The Skywalker Saga appears to have ended with Rise of Skywalker, but if a filmmaker decides they want Darth Sidious back someday, the possibility of his resurrection remains open. The emperor Palpatine could come back from his death in Star Wars: The Rise of Skywalker, but whether or not he ever will is up to Disney and Lucasfilm.