As of July 2016, Sony has updated the PlayStation Network Terms of Service (ToS) to include the following clause for those with inactive accounts:
You may close your Account by contacting us using the details below. We may close your Account if it has not been used for at least 24 months. In both cases, we will not provide you with a refund of your unused wallet funds and unexpired periods of your subscriptions unless we are required to do so by law. After your Account is closed, you will not be able to access the PSN nor use the Products purchased with that Account.
However, Sony seems to have only implemented this clause in the Terms of Service for Europe, not in North America. The North America ToS was also updated in July 2016, but does not contain any language about closing inactive accounts. It merely states why sub-Accounts and Master Accounts can be closed for violating the ToS and that Sony holds the right to terminate an account for any reason, which is typical legalese.
The ToS with the above language is only found on the European Network, as stipulated in the first paragraph of the document:
The PlayStation Network (“PSN“) is provided to you by Sony Interactive Entertainment Network Europe Limited, company number 06020283 (“SIENE“). Prior to 29 July 2016, SIENE was known as Sony Network Entertainment Europe Limited. You must have a Sony Entertainment Network account (“Account“) to use the PSN.
This update to the ToS was first spotted on NeoGAF, but another user quickly pointed out that an update to the European ToS in 2009 stated that Sony would close accounts after 18 months. In reality, this latest update extends the time for inactive accounts.
If you have a European account and haven’t logged in to your PSN in awhile, you might want to do so. In fact, do so no matter where you live. Who knows when Sony will sneak this clause into future ToS updates outside of Europe.