Apparently they have stopped the activation of Combo plan recharges and one can survive on the 40GB data vouchers even after the expiration of the Combo plan. Queueing up Combo plans is of no use now as you can't activate them and neither would they activate automatically. Data consumptions happens only in the data vouchers.
@bobby_kes 351 plan gives 50 GB data at 10 mbps. Rs 251 data voucher gives 55 GB at 100 mbps (or higher depending on the base plan). Why would someone pay Rs 351 for 50 GB @ 10 mbps instead of Rs 251 for 55 GB @ 100 mbps? 351 can't be an addon.