I don't think they trade up for Rivers. But if our 1st round picks are 22nd and 23rd, I could see Danny trading one of them to Cleveland for their late 1st and early 2nd. Something like the 23rd for the 26th and 38th could work if Cleveland could get a player they wanted, and Danny sees more value in trading down.
In that scenario, Celtics would have #22, #26 and #38, plus their own 2nd rounder (#52) and with lots of luck, #45 from Milwaukee. 2nd round pick(s) could be traded or used to draft international players with upside, like San Antonio or Houston usually do.
Quincy Miller/Royce White/Arnett Moultrie with #22
Doron Lamb/Festus Ezeli/Draymont Green/Tony Mitchell/Jae Crowder with #26 and #38
Maybe Jeff Withey/Quincy Acy/Will Barton/Yancy Gates are available at the middle of the 2nd round. International guys like Satoransky, Shengeila or Aldemir could be the best options at that point.
I hope Danny can get his players on this draft, and get gems like Bradley.
Go Celtics!