Ok, the test went as follows...
I submitted turns in the test game until turn 5 was reached, then rolled the game back to turn 1 and un-started it. The result of which was the game reappeared in the "Games Waiting For Pretenders" area of the llamaserver, where it needed to be

I then tested removing Pretenders, changing maps and mods (all seemed ok). After this I then restarted the game and played the first turn of all three nations. (which is where that game is now). Again this went nice and smoothly and to plan. Here's the game logs
http://www.llamaserver.net/doAdminAc...n=showadminlog
06:26 GMT on Monday April 11th Rolled game back to turn 4.
06:37 GMT on Monday April 11th Rolled game back to turn 3.
06:42 GMT on Monday April 11th Rolled game back to turn 2.
06:54 GMT on Monday April 11th Rolled game back to turn 1.
06:57 GMT on Monday April 11th Returned game to the "Waiting for pretenders" state.
But.... (sadly there's always a 'but'

)
I did notice that the admin option to "Un-start game (go back to "Waiting for Pretenders" was available on turn 5. Which wasn't what I expected to see. And a new game (TrojanHorses) that I started yesterday as admin also has the option available on turn 2. So the option to Un-start a game appears to be time based and not turn based as I originally thought. Whether or not it's only time based though I have no idea right now (as the option could appear on turn 1 or within X hours of the game starting).
Llamabeast would likely know the answer to whether the Un-start option is time based or turn+time based. But right now I'm a big question mark on the matter? As the option to Un-start might appear if the game is rolled back to turn 1, but then again it might not.
Of course the other way to restart is just to create a new game and get everyone to send Pretenders again. Although if the game is restarting for definite one way or the other, then there's probably no harm in trying to roll the current game back to turn 1 and see if the Un-start option appears. (as then the worst case scenario is the Un-start option doesn't appear, and the game has to be deleted. But that would happen anyway if a new game is created.)