Question

When do the pages get consumed/license page counter gets decreased in Vantage? 

Answer

If the transaction was processed, even if the final status is Failed, the pages will be consumed.

However, if the transaction has failed before the start of the processing, the pages will not be consumed.

You can find detailed information regarding pages consumption by referring to the following Vantage help article: Administrator's Guide > Subscriptions > How Pages Are Counted in ABBYY Vantage.