The front-end server is responsible for managing client connections. When the front-end server is offline you will not be able to connect to the Dynatrace server. If the back-end server is still online, then I expect that your system profile configurations continue to work as expected while the server collects data. My recommendation is that you get the front-end server back online rather than restoring the system profile to a new server. If you choose to restore the system profile to a new server you will lose historical session data and historical performance warehouse data.
However, if you really need to restore the system profile to a new server while the server is offline you can copy the profiles xml document from <DT_HOME>/server/conf/profiles to the same directory of another offline server.