I purchased the tickets directly from Qantas website and Indigo is part of the domestic connection.
Cool. I assume your domestic legs are part of the international ticket/PNR.
I called Indigo Airlines, they informed me that my ticket has 30kg allowance which was issued by Qantas.
This is correct. This is what Indigo (6E) will see from their end. To be fair, the ability to see 30KG on 6E end is an improvement. Earlier they used to see 15KG as the allowance. Boy, am I glad that is fixed now.
I called the Qantas, they informed me that since it is codeshare with Indigo (and not part of one world), I have to follow Indigo's policy, they won't update my luggage allowance for the return trip.
Depends on who in QF you were able to talk to - someone without proper information/training might say something like this. This doesn't sound right to me. Assuming all the itinerary legs are in the same PNR, which means baggage allowance is applicable for the whole trip (including in/out of the domestic port).
However, in your personal experience, they did honour the higher allowance based on your FF status. This gives me some hope.
Ah mate, I have been doing in/out of India few times a year for few years now in the 6E-QF partnership and I only had issues the first 2 times exiting MAA and BLR.
In the first instance, ex-MAA, I had to get a manager from 6E who was not helpful, but I was able to talk to a very helpful staff from HBA over the phone who tried to explain the policy to 6E staff, who did not still get it. It went to the point where the HBA staff said that she can provide a QF company credit card to charge for excess baggage and I won't have to foot the bill.
In the second instance, ex-BLR, I had to show my QFF WP card and had to involve the Airport Manager for QF at BLR to get my baggage checked-in.
After these 2 instances, I have done more trips than I can count and have not had any issues. So you will be fine. Just keep your QFF WP card handy and hold your ground. Ask for a the QF manager at the airport (if flying out of DEL or BLR) and they can assist. These days, the QF ground staff at IN ports are trained enough that they recognise statuses.
Years back when SYD-BLR-SYD service was commenced, I was asked to go to the back of the Y check-in as I was flying Y. My WP status did not mean a thing. Not a biggie, just the staff did not really understand the statuses back then. Things have improved quite a lot now.