Even though emotionally it is setback, I think, he (nitish) will drop in 4th test to provide more bowling strength as we are struggling to get out the Aussie.
Mostly washie will replace him
Won't be bad choice if they drop NKR for genuine 4th pacer and sacrifice batting little bit but dropping him for second spinner washi would be a terrible choice
To sacrifice fourth pace bowler, i can drop Gill instead of Nitish. He is allrounder better than Gill in batting also has handy in bowling if the ball gets old