Is gst payable on expired pre-gst goods on which no itc was claimed/available?

My client is a distributor of packaged food products, which carry a pre-printed Best before date.

Client has stock of goods acquired against C-Form from manufacturer on which no ITC was available.

Said goods were already expired before GST transistion but Client chose to not write-off as they were hoping manufacturer would consider return and replacement.  This food product is taxable @ 18% under GST.

In 2017-18 the Proprietor of Manufacturing firm passed away and there is no scope to exchange goods.

Now my Qns are as follows:

1. If Client writes off these goods, do they need to pay GST on the same?
2. If yes/no, please quote the specific act & section which clarifies taxability/exemption.