The Yub Nub Ewok happy victory song wasn’t enough to convince me that the empire was finished after the death of the Emperor and Vader. This is an empire that controls the galaxy. How many generals, admirals and moffs are there in the chain of command ready to step up and take command of the remnants. There may have even been many factions after the fall of the core leadership.
Killing Han was clearly what Kylo Ren needed to do in order to go all in on his path to the dark side.