This is fairly common. The mice are able to nest easily back in there. The ignition rotor is an extremely frail piece of plastic and any rotation from the engine breaks it when trying to push through the nest. Here is a post on here from me last year with this very exact same issue:
http://www.irv2.com/forums/f54/major...et-173875.html
Unfortunately, you are going to have to remove the generator from the coach. The ignition rotor is located on the output side of the crankshaft where the bell of the generator (stator) portion bolts to the engine portion. Thus it will need separated. I would also check the windings in the stator as the mice love to chew the insulation along the edges.