You cannot have a pan India answer for this question. Back in the olden days I guess most women did not wear underwear like a panty, but they always wore some kind of a foundation garment like inner skirt or a chemisole.
I am a kerala Christian and I am sure the younger generation born after 1950 surely wear underwear. My wife is 42 and she wears a panty all the time, with a sari, with a salwar and under her nightgown too. She could never think of going out without one. She has been trained to wear one from childhood. One cannot rule out missionary influence in my case. All current generation mallu’s do wear panties, irrespective of religion.
I have traveled a lot in India and found north Indian women wear panties though sometimes under the salwar they do not. In Andhra most mature women do not wear either panty or bra. Many that were used to wearing one as a kids or as a teenager discontinue after they become mothers. It is strange. I know a friend’s wife who is a convent educated woman and I am sure she must have worn panties and bra as a student. But now you would be surprised to hear she wears neither. Well are you wondering how did I know? Well I do visit their house often but have never seen a panty on their clothesline. I asked other people in Andhra about it and I was told Telegu married women do not wear panties as they see it a s kind of sexy apparel.
In south (whole) as far as I & friends know females born before 60 never used panties, in 1980’s they used to wear self stitched cotton panties with out elastic. During periods, since they used to wear long petticoat called LANGA under saree, they were using old cotton cloth ,Langa used has support to hold the cloth, even now in villages you can find this. small girls usually used to wear Long LANGA and short LANGA beneath.As far BRA is concerned, middle aged women usually not wear bra in house only if they go out they will wear. girls only after joining college,wear bra.