More than likely a trade wouldn't happen until the draft where we would trade the rights to the picks after the selections so if MKG were to drop I'd assume that the Cavs would hold onto the pick rather than trade down for 6 and 11.
Logically, I think the trade actually wouldn't happen till Portland selected at 6. In order for the trade to work, the Cavs obviously would have to select the player Portland covets at 4. In addition, whoever this player is would have to be the Cavs' preference at the 4 spot (or a virtually tie with the player they would be targeting at 6). The reason for this is that the Cavs couldn't risk drafting a player for Portland at 4 that they did themselves not want, because Sacramento at 5 might select the player the Cavs were targeting at 6.
So, for the sake of the argument, say the guy Portland wants at 4 is Beal. If the Cavs feel they would like Beal at 4, but would be perfectly happy with, say, Barnes instead, especially if they could also get a guy they covet at 11, then the trade might work. But it would presumably be dependent on (1) MKG not being available at 4 (otherwise, the Cavs draft him and there is no trade); and (2) Sacramento not drafting Barnes at 5 (if this were to happen, the Cavs would simply keep Beal and there would be no deal).
In this scenario, I am assuming Portland's target is Beal, and the Cavs value Beal and Barnes roughly equally, but you could exchange another name for Beal (presumably Drummond), and it would work the same. The main point is that, ironically, both Portland and Cleveland would actually have to prefer the same guy at 4.