Here are steps to find all deceased accounts:
    1. Click Queries > Manage Queries
    2. Select a category that you want to store this query in (Ex: Base)
    3. Click New Query under the Tasks menu
    4. Name the query Deceased Accounts
    5. Set the Starting Query to Base: All Constituents - A
    6. Set the Data Return Type to Accounts
    7. Select Match At Least One Criteria under Criteria Matching
    8. Select UDFs - Constituent from the Browse Fields drop down menu
    9. Select Mailing Status from the list of links
    10. Check Deceased
    11. Click Save And - View Queries