Hi @Dustin Smith ,
Please try creating a new database and moving all users from the old database to it. Then delete again to see if it succeeds.
If possible, we try not to recommend modifying it in ADSI edit because it is destructive and cannot be undone.
Here is a similar thread for your reference: Exchange 2013: This mailbox database is associated with one or more active mailboximport / Cannot uninstall exchange (microsoft.com)
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread