While restoring a replicated database without KEEP_REPLICATION option, SQL Server will remove replication settings by executing sp_restoredbreplication at the end of the process. The 'sp_restoredbreplication' system stored procedure will delete all replication metadata, that is, deletion of 'tr_MStran_alterschemaonly', 'tr_MStran_altertable', 'tr_MStran_altertrigger' and 'tr_MStran_alterview' tiggers (which were created to validate alterations on the replication of tables, triggers, views), disable user tables for replication, and deletion of subscription/publications/articles. Nevertheless, there might be some cases where 'sp_restoredbreplication' cannot be executed successfully and ends up leaving the database OFFLINE. I personally experienced that case and the error was something like this:
Msg 3165, Level 16, State 1, Line 1
Database ‘MyDB’ was restored, however an error was encountered while replication was being restored/removed. The database has been left offline. See the topic MSSQL_ENG003165 in SQL Server Books Online.
Msg 3167, Level 16, State 1, Line 1
RESTORE could not start database ‘MyDB’.
Msg 3013, Level 16, State 1, Line 1
RESTORE DATABASE is terminating abnormally.
Looking into this case, I could see that the cause was a DDL database trigger which existed inside the database. Let me expand on what I am saying. The database had that trigger to audit some schema changes which were supposed to save into an auditing table. Unfortunately, that auditing table did not exist in the server where the database was being restored, and the deletion of objects of replication settings were not completed, which means that 'sp_restoredbreplication' was not executed correctly. Consequently, the restoration was stopped and SQL Server decided to leave the database OFFLINE.
In order to restore a copy of this database, we need to disable all DDL database triggers before taking its backup. Only then will the database be restored successfully. The other method to deal with this issue is to change the status to ONLINE manually after the restoration finishes unsuccessfully and also execute 'sp_restoredbreplication'.
To sum up, we need to proceed with more cautiousness while working with databases linked to replication. That is all for now. Let me know any remarks you may have. Thanks for reading. Stay tuned.