Kurdistan
The end in Vietnam was not this bad because there was an organized resistance by the S Vietnamese which, although quickly unraveling, gave time for the palefaces to make their escape. The situation in Iraq is now so chaotic that the best we can hope for is widespread internecine fighting to cover our retreat.
There's another option: Choose sides.
Kurdistan is relatively quiet; they don't seem to hate us as much as the Shiites or Sunnis do. They want to be independent, anyway. By my lights, they ought to be.
A strategic re-positioning to Kurdistan puts a NATO ally at our back, a less hostile environment, and possibly some help on defense... and time to leave by the back door.