Actually you can use any of the three parts of a planetary gear system as input, and either of the remaining two as output. Depending on which combination you select, you either get a reversal of the direction of rotation, or not. For example, if you drive the sun gear, and use the annulus (the outer ring) as output, you do get a reversal. If you instead hold the annulus fixed, drive the sun gear, and then use the rotation of the planetary carrier as output, the direction of rotation will be the same. IOW, you'd attach the output shaft to the frame (missing from the animation) holding the yellow planetary gears:
edit: I watched this animation a few more times, and the planetary gear carrier is not actually omitted, it's just the featureless gray structure behind the planets.
You can also use a double set of planetary gears to generate a non-reversed rotation of the annulus relative to a driven sun gear.
I don't know what P&W is doing, but if the fan counter-rotates, the requirement is impossible - if the gearbox froze (and things didn't just go to pieces), the fan would start to rotate backwards. If P&W uses one of the non-reversing arrangements, then the fan hypothetically would still turn (at the wrong speed), but would still be subject to a huge shock as is speed suddenly changed. I'm also not sure if any of the non-reversing configurations of planetary gears could freeze in a way that didn't just prevent rotation at all.
Still, there are plenty of aircraft with critical gearboxes (all multi-engine helicopters, any turboprop), that I can't see that surviving a total failure like that is likely to be a requirement.
[Edited 2010-02-12 21:40:13]