Importing the old world as a separate world is vastly better than the copy-pasting I suggested. Glad to hear the original nether is now restored.
For reference, here is the original Minecraft thread
I sse that the old server was started September 22nd 2011, and was up until at least Dec 2016.
There is a zoomable map of the server last updated 2014? at http://minecraft.hamsterrepublic.com/ohrss/
Looks like I haven't played MC since 2015 but apparently already largely stopped in 2013. I'm still resisting breaking such a successful streak by joining the new server! So instead I watched Baconlab's tour of the old world, loved it.
Do the teleporters in the Teleportation Station in Creeperton still work? There used to be one to the huge Walled City of Wallachia (founded ~2014). (In Discord I repeatedly referred to this as Farington; I misremembered the name. Wallachia isn't marked the map and I don't remember its location). I believe there is also an impressively long nether-road to it.
Of course there's heaps more to see on the old server, including notably Nigel/Wozzeck/Jabbercat's MegaCathedral, a huge (built) nether fortress which I can no longer remember how to reach (it was at the end of a long nether rail, the start of which was I think intentionally difficult to find), an underwater extension of New Jerusalem and not to mention everything James has been up to for the last 7 years which I don't know about! The (original) Cathedral also has a basement but IIRC it's just a big void.