But we don't know if Palpatine comes back to life. All we know is Ian Mcdiarmid is coming back to reprise the role. It could be one of those android emperor stand-ins, a force ghost, who knows?
Also, I'm not sure Luke saying "No one is ever really gone" is meant to be taken literally. It could mean that the people and experiences you have stay with you all your life, even if they die/go away. But, again, we don't know the context of that line.
Star Wars trailers, especially recent ones, have been very deceiving when it comes to plot/theme.
We'll have to wait and see, but RLM's reaction seems a bit... premature.