This article suggests the Kings wont pick up his option.
Instead of giving up two picks, why not go all in with the rebuild? They have two horrible contracts in Salmons and Hayes. Both have 3 years left. If it is time to rebuild, Danny could take Tyreke and the two bad contracts for Pierce and Moore.
The Celtics then have 3 good young guards in Tyreke, Bradley, and of course Rondo. You draft two athletic forwards to team with JJJ. Hayes can play PF while KG comes back for one or two years to play center and be the mentor to all the young guys (and also to help keep the team respectable)
After one year, Amnesty the 32 year old Salmons. After two years you can do the same with Hayes if he is not working out.
They can go with Cousins, Thornton, Jimmer, Thomas, and the #6 pick for the future while Pierce makes them more of a factor this year.
The Celtics:
Rondo Salmons
Bradley Evans
Green Draft
Hayes JJJ Draft
KG Stiemsma
Not the best roster ever, but if you are going to build around Rondo, you need a good guard to run with him and you need really athletic forwards to run the floor.
Danny would still have great cap space when KG came back off the books and he amnestys Salmon.