Mirrored databases are disconnected after you restart the database mirror in SQL Server

Issue:- 
Mirrored databases are disconnected after restart of SQL instance due to 

• Server Hang , 
• You end the process of the SQL Server secondary instance by using Task Manager
• Network Issue 

in SQL Server 2005 and above.

Resolution 1:

In above image you can see DBA database is in Disconnected mode.
How to over come on this ???
T-sql commands.

First need to find endpoint name of mirrored server.

SELECT name,type_desc,state_desc,role_desc FROM sys.database_mirroring_endpoints;

On the principal database, execute the following SQL script to stop the endpoint:
         ALTER ENDPOINT <Endpoint Name> STATE=STOPPED
     eg: ALTER ENDPOINT Mirroring STATE=STOPPED 

Execute the following SQL script to restart the endpoint:
         ALTER ENDPOINT <Endpoint Name> STATE=STARTED
     eg: ALTER ENDPOINT Mirroring STATE=STARTED



Resolution 2 : 

Drop and re-create the database mirroring endpoints on both servers.

First need to find endpoint name of mirrored server.

SELECT name,type_desc,state_desc,role_desc FROM sys.database_mirroring_endpoints;



On the principal database, execute the following SQL script to drop the endpoint

drop endpoint <END POINTNAME>
go

On the principal database, execute the following SQL script to Create Endpoint :

CREATE ENDPOINT Mirroring
STATE = STARTED
AS TCP ( LISTENER_PORT = 5022 )
FOR DATABASE_MIRRORING 
(ENCRYPTION = DISABLED,ROLE=ALL)

GO

Use correct Encryption , else DB would be in disconnected mode 

Thats it :)

More :

➤ Steps for Configuration of Mirroring setup