Unless the device is physically out of space for storing things, there is no excuse for putting up a modal loading indicator because of a server-only problem.

As a general rule, every single edit should be able to return control to the user immediately. If the network can’t be reached, save locally and attempt an update in the background (showing a small, unobtrusive annotation that an update is pending, as opposed to a screen-erasing obnoxious progress popover). And definitely don’t erase everything the user did if the network ends up being unreachable.