Exchange 2013 Mailbox DB corrupted, Need to delete user account from AD directly

Hi Exchange experts, we have complex and struggling scenario here.

Target: Drop dismounted database completely in order release disk space and complete migration.

symptom: EAC when attempt migrate healthy user mailbox to another mailbox database, occurred error "Cannot open mailbox /o=xx/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=EX2013MBX/cn=Microsoft
System Attendant" , suspected in the database list possessed 1 dismounted database, therefore attempt to DELETE it, also need to vacate disk space as exchange server already left 150GB.

We are using Exchange 2013 and the initial setup is only 1 mail database that include all the client mailbox, so it is heavily corrupted when the EDB file hit to 800GB.
Results of repair corrupted EDB is failed therefore we create a new mailbox database and mounted it on exchange. the corrupted EDB leave it as dismounted.
And then we delete AD User 1 by 1 and then recreate with same login ID, and point to new mailbox database. (since we tried EAC to migrate mailbox, also used "get-mailbox -database "Mailbox Database 0211395451 | new-moverequest -targetdatabase opsexhgdata" in EMS, both error as corrupted mailbox might not able to migrate anymore)

Now we are stuck at domain administrator account, "Cannot perform this operation on built-in accounts." error pop-up during attempt delete administrator account (to delete mailbox and create to new mailbox database) currently we are unable to use EAC to migrate any user, and also cannot drop the 800GB corrupted EDB file due to built-in administrator still possessed mailbox in the corrupted mailbox database. 

Any advice from exchange experts?
Golden PapaIT SUPPORT ENGINEERAsked:
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Hasin Ahmed ChoudharyExchange AdministratorCommented:
And then we delete AD User 1 by 1 and then recreate with same login ID, and point to new mailbox database. (since we tried EAC to migrate mailbox, also used "get-mailbox -database "Mailbox Database 0211395451 | new-moverequest -targetdatabase opsexhgdata" in EMS, both error as corrupted mailbox might not able to migrate anymore)

You could have use Database re-homing feature to use existing AD account. It just change the database to new one.
As you have create new Ad account, Understand you are least worried about data on on Old<dismounted database.

Does the dismounted database only contain Built-In Admins account ? Is it Exchange Admin account ?

How about you just try to re-home mailbox.

Set-mailbox <Admin account> -database <New Database name> . It will create new mailbox for that Admin account on new DB. IF you managed to clean old DB and mount it , you can use restore feature to copy all data to new mailbox.
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MAS (MVE)EE Solution Guide - Technical Dept HeadCommented:
Agree with above it was easier to reconnect the user instead of recreating.
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Golden PapaIT SUPPORT ENGINEERAuthor Commented:
Hi Hasin, thanks for your advice!
the command is work as my administrator mailbox is point to new mail database!
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