Ok.....if the mirror glass is cracked and does not give u a clear view to the rear then yes it will fail...But if u can still see pretty good then u might just get an advise....
As for having 2 rear facing mirrors....the o/s door mirror is compulsory,,but u can have either a n/s dorr mirror or an interior mirror so for instance if ure n/s mirror is missing and u still have ure interior one then u wud pass and vice versa