I was asked in interview, if you operating in high security and ur transaction is not commited at the mirror and your mirror goes down and it is not yet commited on principal, how would you recover your transaction?

AFAIK you will have to increase a size of your database on mirrored db manually this will not be reflected automatically, but yes their are changes in your table structure or it will be applied automatically. If you alter db size, you have to change it manually in replication too.

Hi, One shoud not have to worries for this as changes in structure are recorded and applied to mirror automatically.