No, you shouldn't need an active connection, just a simple ftp server (I used to run cerberus ftp, try it). When you're not connected to the internet, your address is 127.0.0.1
Anyway, adding the ability to use a local dir would be useful and simple.
Also, I figured out a new way to implement a good internet sharing server. I've been learning php and mysql in the last months, so this is how I would do it now:
DB should pretend to be a web browser, that is, it should communicate with a web server sending http headers and messages (not difficoult to do)
The server would be the web server of darwinbots.com.
DB would talk to the server to require a robot or to request saving of a robot; every request to save something should carry a security code (for example, a hash of the robot dna) to discourage intrusions and misuse.
On the server side, all requestes would be processed by a php script, retrieving and saving robots to a mysql database.
The system would be much more flexible than it is now, allowing a centralized management of the server files, separate groups for each kind of sim, and so on. I could write the php/mysql server part, if someone wants to write the client code.
I definitely think that a good sharing feature should be present in any major future release of DarwinBots.