gear box fault signal appeared. 2 weeks later i'm driving along and all the sudden there's some loud noises and the drive shaft snapped  right off. Any ideas what the part is that needs repair (obviously other than the a new drive shaft). I'm wondering how this happened and how much it's going to cost me to fix.

hi

off that description, which is pretty vague, could be anything and the two may not even be connected

you need to get it checked at a garage, drive shaft could be just a failed cv joint and its fell apart, second hand drives shaft are a plenty on ebay and not that expensive

you could try jaguar auto reserve, had parts from there and are very good and reasonably priced https://www.autoreservejaguar.com/

as for the gearbox fault warning, you need to get it plugged in, could be something as simple as a abs sensor or low battery

cheers

Joe