Maybe Barry will make a deal with a Time Wraith and a Black Flash to come and put Savitar out of everyone’s misery.
(Although at this point, the surest way that Flash can guarantee a different future is by attempting to fix something that already happened.)
Or maybe all this will be revealed to be Savitar’s Flashpoint universe, which he reverts back to some original timeline where he’s just a mopey dude and not actually messing around with calcified fragments of the Speed Force.
As far as what Barry could do to defy expectations, he could — oh, I don’t know — choose not to fix a problem by going back in time to change things.