Not, not intentionally on the server until mirroring support is added: Request: Mirror federated storage locally [$20] · Issue #8459 · nextcloud/server · GitHub
See also Mirroring of two nextcloud server
The way it happens now is the federated file and folder shares will sync to the client devices on both servers, but the server copies will only cache on the original server. This means when the server goes offline to client devices sync’ed copies will still be there.