1. definately, thats what the timing signal is derived from
2. the bolt needs to come out, or you wont get it fixed at all mate. the sensor is critical and probably bolted to 25nm but thats irrelevent now the head has snapped off. And easy way to remove a snapped bolt (if you have the room) is to drill a hole down the centre of it, and bang in an allen key of the same size as the drill, pick something about 1/3 of teh size of the bolt, when the allen is hammered deep into the hole, it gets a great bite, and is hard as a whores heart, it will not bend or flinch and the bolt will screw out.