If you let a Phase II exemption expire would we need to complete a revoke exemption form? Thanks!

From the instructions to the Designation of Exempt Person form:

"A bank may, but is not required to, use this form
to notify the Treasury that the bank has revoked the
designation of a customer as an exempt person."

So you aren't ever required to report a revocation, even if you let one expire.

Was the failure to complete the biennial an oversight? If so, you need to call FinCEn state the facts and ask for a backfiling determination. They might just let you send in the biennial renewal or they may make you file some CTR's, or both.

Be nice and they might work with you!

The number is 800.800.2877