I wouldn't voluntarily refund, if you are making refunds then the buyer should open a case of item not received.
Also how were the items sent, if the labels were provided by ebay eg were simple delivery items and had market place seller on them, then it is ebay who refund not you. Again the buyer needs to open a case so eBay can deal with it.
If you provided the labels off your own back then you would refund, once asked via a INR.
It may well have been that the items have been miss sorted by Royal Mail hence the delay etc.