Mirroring SQL Server 2008R2
Does automatic fail over happens in mirroring if the connection between witness server and principle server is lost for some reason.?


No automatic failover does not happen in this scenario as the current principal will still have a quorum forming a partner-to-partner quorum. Without a witness, automatic failover is not possible - ONLY Manual failover is possible.



This is explained in more detailed at How a Witness Affects Database Availability ?