I mean... not... quite? Voldemort just wouldn't die if his Horcruxes still existed. Palpatine can be killed - you just have to make sure that his spirit is in his body when you do so.
However, the whole 'can force his soul from his body' thing... it kind of gives them carte blanche to reuse the character in the future.
Don't think he's got any clone bodies left? That's another thing revealed by the novel: Palpatine Junior is a 'perfect' clone of Palpatine, just discarded as a vessel because he had no Force power.
So, other things from the novel:
-Leia is dying throughout Episode IX - her body was damaged because of her little jaunt into space in TLJ. Luke is whispering to her throughout to try and persuade her to let go and join him in the Force. She doesn't want to until she can see Ben.
-The dyad concept is not explained very well, but it turns out Palpatine and Plagueis had tried to form a dyad and failed. Palpatine had wanted to form a dyad with Anakin.
-Kylo interrogates Chewie aboard the Star Destroyer by invading his mind - Kylo sees the past from Chewie's perspective. Apparently kid Ben called him 'Uncle Chewie'.
-Lando had a daughter who is missing. The First Order deliberately targeted the children of Rebellion heroes and his daughter is remarked to have become a Stormtrooper. Not stated to be Jannah.
-Rey had already started constructing her own lightsaber.
-Rey had learned Force Heal when repairing the Skywalker Saber - she used it to repair the broken Kyber Crystal.
-Ben turned back after Rey stabbed him because he realised that everybody he had confronted had tried to help him: Han, Luke, Leia, all three of them sacrificed themselves to try to help him. Rey was prepared to give all of her life force to Ben also.
-Cloning is talked about a bit: Plagueis had explored cloning as a method of prolonging his life, but that failed. Palpatine obviously cloned himself. The body he was inhabiting had not been finished and so began to rot when he inhabited it. Another result of his cloning project resulted in a 'perfect' clone that was named as his 'son' - this 'son' had no Force Power and was not suitable as a vessel as a result. In other words, Rey would technically be Palpatine's daughter, not his granddaughter.
-Finn's Force-sensitivity is never explicitly stated but implied much more heavily. He even senses Rey coming back to life.
-There is a moment where Rey mind-tricks Finn into returning to Ochi's ship on Pasaana, as Kylo Ren approaches.
-Apparently Rey and Rose are good friends.