What happens if Serv-U looses ODBC database connection?

Hi

I was thinking about migrating our Serv-U FTP server's user database from the normal "Domain Users" file, to a MSSQL2012 database.

My concern is what will happen if the database for some reason goes offline.

Will users still be able to log in?

And if so, how - via. local cached DB?

Thanks for your help