The Jays should not trade Dickey or Buehrle. How are they going to replace those innings? They can't and won't. Just hold on to them and fix the actual problems with the team.
My guess is Happ will be traded and Sanchez will be pencilled in for the #5 spot, which is why Estrada was probably attractive to AA since he can be used as insurance in case Sanchez struggles/gets hurt/needs more time in AAA. If you're going to have at least 2, if not 3, young starters in the rotation, guys like Dickey and Buehrle are that much more valuable. I'd actually prefer adding one more 200 IP league average type guy instead of using Sanchez (think, Jeremy Guthrie type) to put in the #5 spot, but not too many of those floating around.
If AA has any last gasp miracle in him, he can turn Happ into a quality 2B. I don't know how he could possibly pull that off, but there has to be some malcontent 2B with talent somewhere that another team wants to dump, or a team with an extra 2B they could move. The Cubs are too smart to do Valbuena for Happ but something along those lines is sorely needed. I could live with the Bautista/Pompey/Gose/Pillar/Dirks OF in that case.