I still think Hall starts and plays 28mpg. Demin will be the primary PG when Hall is out.
Hall is a good player, good enough to play even with this talented roster. Further, he brings experience and continuity that is necessary and will help the younger and highly talented players.
Hall will help in a lot of little things that are often the difference that makes a team of talented players become a very good basketball team. With him facilitating I think it is likely there are fewer turnover, guys will get the ball in the best position for them to score, team and ball movement will be more consistent and purposeful etc.
It is easy for folks to get caught up in the shiny new things, but a few of the old guard stalwarts will be useful in keeping the ship pointed in the right direction. As KY brings in these highly touted one and dones or other highly recruited kids outside of BYU’s historical recruiting base, I expect he will still rely upon the few historical “BYU guys” who are typically older and more mature to provide that leadership. Having one of those types at PG will very useful for him IMO.