Does this meet the goal?

Your network contains a single Active Directory forest. The forest contains a domain controller and Active
Directory Federation Services (AD FS) servers that are deployed to virtual machines. The virtual machines run either on-premises or on Microsoft Azure.
You have Azure AD Connect deployed on-premises. The Azure AD Connect database is installed on an on- premises instance of Microsoft SQL Server 2014.
Last month, an Azure AD Connect server experienced a hardware failure that caused an Azure AD Connect server to go offline for several days.
You need to recommend a solution to reduce the outage window when hardware failure occurs on the Azure
AD Connect server.
Solution: You deploy a new on-premises Azure AD Connect server that uses a new SQL Server instance. You set the Azure AD Connect server to staging mode.
Does this meet the goal? installation, you can enable a server to be in staging mode. solutions include mirroring and Always On. operations/

A.
Yes

B.
No

Explanation:

Azure AD Connect sync Staging mode can be used for several scenarios, including:
High availability.
Test and deploy new configuration changes.
Introduce a new server and decommission the old.
Have a spare standby server – staging mode
If you have a more complex environment, then having one or more standby servers is recommended. During
SQL Clustering would be needed for high availability.
Note: SQL High Availability
If you are not using the SQL Server Express that comes with Azure AD Connect, then high availability for SQL
Server should also be considered. The only high availability solution supported is SQL clustering. Unsupported

References: https://azure.microsoft.com/en-us/documentation/articles/active-directory-aadconnectsync-