They are not going to want veterans in their current state, so that leaves us with young guys and draft picks. I'd give up pretty much anything for him. Big, skilled, elite defensive bigs are pretty rare. I'd do next year's pick, KO or Sully, and Avery Bradley and even something else. Trade Rondo and Green for younger assets/picks and do a proper rebuild.
Remember, Nerlens was a shoe in for #1 last year before he hurt his knee.