If Irving leaves
Plan A, I expect the Cs to keep Rozier. We have seen in the past that RFA often do not get the offers they expect. A team like the Suns could always give him an offer that the Cs can't match but I'm thinking that is less likely given his play this year. If Rozier is retained I would expect the Cs to start Smart,Brown,Tatum,Hayward, and Horford (assuming he takes option). Rozier then becomes a heavy usage 6th man like Smart has been most of his career
Plan B, If Irving and Rozier walk then I would try to trade up for Garland in the draft and look to sign a stop gap Vet. IT would be great but I worry that he would be a distraction. Other options could be Shelvin Mack, Trey Burke, or Jeremy Lin
In both situations if the Cs can't trade up for Garland I would look to draft Markus Howard or Shamorie Ponds. I don't project either player as a starting NBA point guard but think they both can prove to be valuable bench players providing scoring off the bench.