I like Rozier, but is he the kind of player you can give the ball to at the end of a game to create his own shot and win the game? I dont think so...at least not yet...What he is right now is a solid starting PG who works on a team with other scorers/stars. he goes hot and cold.
Kyrie Irving we know has the ability to take over a game when all else fails.
that said, if Kyrie left I would want to keep Rozier. I think Danny wants to hedge his bets. While there is a solid chance Kyrie stays, you dont want to risk getting rid of your plan-B if he does decide to leave.