That sounds like a great crossover you fashioned there :D
Regarding the femur, that's a great question. To give you a simple answer, the "indestructible" only refers to it breaking when you fumble an attack roll. That can't happen. So out of combat, you can rule that it can be ground down in a mill or something (if you want to). Otherwise, to give it a bit more flavor, I suggest that you must bath the femur in the blood of an innocent to make it brittle for 1 day during which you can destroy it :)