A return filed with an expired ITIN will be processed, but any credits claimed applicable to the expired ITIN will not be allowed. The taxpayer will receive a notice from the IRS explaining the change(s) made to their tax return and that the ITIN must be renewed. Once the ITIN is renewed, any credits previously not allowed will be reconsidered at that time. Until the ITIN is renewed, the taxpayer will be subject to interest and penalties for any tax owed because of disallowed credits.
Once an ITIN is assigned, it belongs to that taxpayer, unless the ITIN has been revoked. When an individual renews their ITIN, the previously assigned number is renewed.