Photo Credit: [Star Wars: The Last Jedi] Lucasfilm
With Snoke out of the picture in Episode IX, but at the same time leaving his entire story untold, I believe we will see more about him posthumously through his plans for the First Order.
I think that as he learns to command the machine that is the First Order, Kylo Ren will stumble across holojournals that detail exactly what Snoke had planned for his organization. Another superweapon perhaps? The key to a forgotten Force mystery? Maybe even a secret army of clones or droids just waiting for activation?
Even without Snoke being present, it stands to reason that Ren will benefit from some assistance as he takes on the mantle of leadership, and with Snoke existing in holographic form, this gives us the viewers a potential gem of an interaction as Ren learns things about his master that he’d never known.
Not to mention that this story could greatly benefit from some holocron exposure. We’ve seen holocrons in Star Wars: Rebels, and to have one appear in a live-action movie would be a great way of further tying together the Star Wars saga.
It is possible (given the lore of Star Wars) that Snoke had a contingency in the event of his death, perhaps a cloned body at the ready (similar to Palpatine in Legends canon) or maybe he even possesses the knowledge of how to keep his consciousness intact in dark side spirit form.
Either could work as a way to see his plans and goals realized in a galaxy without him, however if he were to return in cloned form, it would be amazing to see him try to exact revenge upon the apprentice who betrayed him.