You should call the Oregon Department of Revenue to verify that you can mail Form OR-243 by mail with the tax return. They have specific requirements for this form. It appears a death certificate has to be attached.
if you are filing by mail, write: Deceased, the taxpayers name, and the taxpayers date of death across the top of the final tax return.
The Oregon State Department of Revenue has this information about Form OR-243:
Return this form to Oregon Department of Revenue 955 Center Street NE Salem, OR 97301-2555 Form 243, page 1 of 2.
For questions regarding the submission process, contact the Oregon Department of Revenue via phone at 503-378-4988 or email questions.dor@dor.oregon.gov. It's important to ensure that all required documents are attached to avoid processing delays.
To submit Form OR-243, mail the completed form to the Oregon Department of Revenue at the address provided on the form. You can also fax the form to 503-378-4991.