What is the accounting treatment for inventory reversed in case the goods have disappeared or gone bad, in accordance with IAS 2 on inventory?

A "theft expense"account should be opened up and the amount transferred from cost of sales to this account if a perpetual inventory system is used. If a periodic system is used, it should be transferred directly from inventory to the theft expense account separately from any inventory adjusment.

You should Debit Other expenses and credit Cost of sales with the amount written off. This is because the expense is no longer classifiable as "cost of sales"