Crowder is a free agent. A restricted one, but it's not impossible he gets an offer the C's don't want to match, so that's the first thing.
Secondly, a rookie isn't likely going to take a lot of minutes initially, even on a mediocre team. But if and when he does, and Crowder is still here, you will also see a cut in ET's minutes, and down further in the guard rotation, in addition to Crowder's. Say the draftee ends up earning 25 minutes a night -- I think those 25 minutes will come from Crowder, ET, AB, Smart, and IT. ET will play more PG and SG, which means a little less for the other three guards.
James Young is the one who really hopes we don't draft a SF. His nonexistent minutes will never return, and will need a trade to see the court.