All the pvt telecom operators will become 4G only because IUC will become zero from 01.01.2021. In bill & keep system when there will be no IUC gain from other operators it will be costly for operators to maintain circuit switched network of 3G & 2G. Moreover, in 4G raising ARPU of customers is easy.
Only BSNL as part of their public service obligation might continue to operate on 2G. So all those customers who don't have smartphones and not planning on to get one eventually have to port into BSNL to continue using their old analogue 2G phones.
Meanwhile, at our place at Santragachi, West Bengal, Vodafone is having terrible 4G VolTe experience...so much so that my friend can't make calls on it. He has to deliberately keep his Vodafone SIM on 2G only mode just for the calls to get through. Shows the current state of affairs for Vodafone network.