The wikipedia article explains the deets, but basically yes, the turbine at the back of the engine is connected to the fan at the front of the engine, and the compressor and whatnot, and the gearbox somewhat decouples the speed of the former and the latter. It would be a bit of a shame if said gearbox fails in flight, of course.
Without knowing a lot about geared turbofans, it would be cool to have a gearbox bypass such that if the gearbox fails, the engine could stop, engage the bypass, and restart in an emergency mode that's less efficient but gets thrust.
i know nothing about turbofans, geared or not, but i would guess that any kind of 'failure' of a gearing system at jet engine speeds means the entire thing is exploding, not just failing over to a backup system.
