If you have a broken pinion shaft, the car would not move.
I snagged this pic from google of the front pinion shaft:
(Ignore that the pinion is reversed in this pic. This was for a VW Vanagon install, which required a custom reversed drive setup)
If that shaft breaks, then the whole trans will destroy itself.
In all my years with modified Subaru's, I've never seen anyone break the pinion shaft. I've seen LOTS of broken pinion gears, but never a broken pinion shaft.