With Kohli not in the mix for 75% of the test series, I would rather opt for Vihari over Jadeja and rely on Vihari's part time off spin for the fifth bowling duties. Vihari is more solid and possesses better technique than Jadeja. I would get in Jadeja only if the pitch is going to be a true spinners track (not sure if Australia would give us such a track this time)
As far as the recent years are concerned, we would mostly be playing on drop-ins so I don't expect the ball to seam around except for the D/N Test in Adelaide. Yes, Gabba is quick and a bouncy track but let us not forget the increasing heat in the Australian summer so it would most probably dry out till India plays over there. So, I would rather have Jadeja and Vihari together. I think we've done this mistake on our last tour to Australia where Vihari was the only spinner we played and we lost that match since Nathan Lyon got around 10 wickets in the match. I would rather want to play this line-up in Kohli's absence
1. Mayank
2. Rohit / KL Rahul / Prithvi Shaw (I rate neither of them being a match winner for Tests)
3. Pujara (don't ever keep him out)
4. Rahane (in Kohli's absence there is no choice but to move him up)
5. Vihari (I think he has played quite a few times on this position in First Class)
6. Pant (Probably the only Keeper in the squad who has performed previously)
7. Jadeja (He should somehow get a go initially)
8. Ashwin (He did perform brilliantly the last time around and him playing with Jadeja strengthens our bowling)
9. Shami
10. Ishant (if fit)/ Umesh
11. Bumrah
Btw is Saini available for the Tests? If yes then just give him a go instead for Umesh. He has actually improved a lot in recent times and definitely deserves chances.