If you do a new map, I would scrap everything from this map and reset.
Alliances would always be reset with a new map, whether it's a restart or multiple worlds. They'd be trickier with multiple worlds, but only if users could play in multiple worlds (which I don't think is a good idea anyway).
With a new map, I may have have spawn "hubs" on every continent. Then, each new country could join within 50 pixels of a spawn point, or within 100 pixels of two other countries. So, placement is going to be tighter, but it will start in clusters around the map.
I think there would be enough players at a restart to make that work well. I'll be sending a broadcast to about 300 accounts (at this point), so hopefully a good portion will sign up. There were obviously a lot of people who joined and then never played, but I don't have a good idea of the percentage without writing a script to look at the data.