Rise of Skywalker official poster

Come up, Jedi. 

This is the primary official poster from the Rise of Skywalker.  That includes a dueling Rey and Kylo Ren, looming massive is the Emperor himself:

The return of Ian McDiarmid to the Star Wars franchise as Emperor Palpatine sounds fairly superior. 

All of us thought he died when Lord Vader threw him down the shaft in The Return of the Jedi. 

How did he survive?

Latest in universe books have steered there was a contingency plan within the occasion of Palpatine’s demise – how does all of it come collectively?