After a database has been split for the purpose of networking, how can you unsplit it for the purpose of taking it offsite?

Firstly make a copy of your front end and back end databases.

With your copies you can do one of two things
1. Keep your database split and use the Linked Table Manager to change the table links in your front end so that it links to the copy of your back end .mdb

or....

2. In your front end delete the linked tables in the database window and select File, Get External Data and Import... and you can import the tables and their data from the back end .mdb

Hope this makes sense

Sorry but the above assumes you are taking it off site to work on it as a stand alone and not via remote connection. If the latter is the case then you probably getting into the realms of database replication.