I don't think he'll die necessarily but with the end of the State of Zhao, his role as a general will pretty much be over. Maybe he'll be imprisoned and he'll be consulted for future battles and stuff because people will want to know his opinion.
I don't think there's necessarily going to be a final villain in Kingdom, mainly just a final big war against Chu where Shin, Mouten, Ouhon, Kyoukai etc. are allowed to flex their strength against the mightiest state, but there's not necessarily going to be some final villain type character. Maybe Kou En of Chu will be the final general they face alongside Renpa and Karin.
I didn't m3an as Villain, Kingdom isn't stereotype manga where it can divided into black n white. For eg Riboku just happens to be on the opposite side of story trying his best to save his country.
Bt i meant the biggest hurdle in Qin path to converging the entire China and that is so far undeniably Riboku. The amount of connection, history and buildup he has the same seems True since EoS.
And i disagree with him getting prisoned or something of that sort. Since Shin doesn't spare his opponents if they met in battle and that battle is destined since the start. Shin has quoted this many times he will the one to defeat Riboku and the author also has hyped/highlight3d his physical strength for him to not have one vs one confrontation with Shin.
I think better option here would be Riboku somehow escaping and then joining another country like General Rinpa used to do, he would come back as stronger or he dies here in this battle.
Edit-Also Shin isn't so good strategically yet to match Riboku at this point in story, another reason why their fight can't happen yet.