In what way would you like to handle the error that the DB is down?

As for the exception you're currently getting as a result, what DBI connect attributes have you configured?  The following snippet

            ...
            # use the parameters the user supplied 
            else {
                require DBI;
                $self->{__DBH}{$name} = DBI->connect(@{ $self->{__DBH_
+CONFIG}{$name} });   # DBH.pm:42
            }
[download]

apparently raises an exception, so my suspicion would be that you've somehow set RaiseError => 1.

Maybe you could force a stack trace to get more detailed info on what exactly is triggering the connect, so you know what to put eval {} around?