Oh, I see. When you said the groups split I thought you meant they were still fully in the same world, so if one burnt down a tavern then the other group would also come across a burnt down tavern, rather than forcing an actual world separation at that point.
If I've read the forums correctly I believe that what you want, then, will already be a part of the online setup. I could have read all of that wrong, though, but it was in response to a thread where I had asked about something similar where you might be, say, GMing a realm multiple times like at a convention or the like.
See if
this thread answers that for you or not.