Australia need two things to win the Ashes. A reliable middle order and a good swing bowler that can take advantage of the conditions in England.
Head seems to be a reliable middle order batsmen at the moment. Handscomb is iffy and Shaun Marsh is Shaun Marsh. Khawaja is a good number 3 and is versatile enough to open the batting if needed. If Australia find two openers and Warner can’t slot back into the team as a opener I would consider playing in the middle order. I think Warner would adapt playing the middle order. I also would consider giving a call up to Patterson. Patterson is a reliable middle order batsmen Australia needs.
Regarding the bowling I would play someone like Sayers or Siddle over one of the big 3. Sayers would a perfect bowler for conditions in England.
My hypothetical Ashes 11:
Renshaw/Burns/Warner
Renshaw/Harris/Burns
Khawaja
Smith
Head/Warner/Finch
Warner/Patterson/Head
Paine
Cummins
Lyon
Sayers
Hazlewood