Yes, NSA is intelligent and caches data locally until a connection is available to upload data to the Nalpeiron servers.
If the client application is offline, the analytics data is cached locally. The cached data is then sent to the server when an internet connection has been established and the application is run. When a connection is available the cached data can be flushed manually sent to the server by an API call to NSASendCache. Please see the NSA client API for details.