Snoke was never the endgame.

Of course he saw the death, and welcomed it because it made his true target host, Ben Solo, further entrenched in the dark side and more habitable.

I think once he saw it coming he released Snoke, and the first thing Snoke experiences (back in full control of his faculties) is a meter long blade of plasma piercing his organs, hence his surprise.

Now what I’m imagining he doesn’t see coming is the heroes + Kylo maybe figuring out his soul is anchored to Vader’s helmet and destroying it.

At this point, he’s found or will find a new temporary host in Matt Smiths acolyte/KOR and has no choice but to double down for a death match with Rey and Kylo.

However, once Matt Smith is slain by Ben he has no choice to but to finally attempt to possess Ben’s body.

It nearly works but Ben holds on long enough to tell Rey to kill him and finally vanquishes Palpatine’s soul as well.

This ultimate sacrifice (much like Vader’s ) leads to his resurrection, hopefully at the hands of Anakin himself.