Demin isn't going to play 40 minutes, they'll want to keep him as fresh as possible for the end of the year, and remember that FR above all others can get worn down by season's end and plateau.
For another thing, teams like to have multiple ball handlers on the floor simultaneously. You saw some lineups last night with both Demin and Crawford, for example. Near as I can tell, Hall and Demin played well together in the scrimmage.
Demin, at least last night, showed he's capable of catch and shoot.
You could argue that while Hall probably wasn't our best player last year and was outshined in the advanced metrics by guys like AK and Saunders and Fouss, he was probably our MVP and the one guy we could not afford to lose. That guy isn't just going away, it means he knows how to contribute. Guys who can floor general and get a team into its offense aren't just pulled off the street. He's a leader and has the potential to be our clutch closer as well, as he has shown multiple times in the past.
Hall is a guy that knows how to play with Fouss and we'll need that weapon. Coach would be an idiot to just ignore Fouss' abilities in the post. Demin may not be as adept at that part of the game. Bringing in Hall and Fouss to run a different offensive style should be something we take advantage of to mess with other teams.
I don't think this is going to be one of our bigger problems to be honest.