Ok. Here's my take on pins.
If the splines on the pinion shaft are not worn, the splines in the coupler are not worn, the shaft is perfectly aligned and the torque tube is perfectly aligned, the pin will not shear.
A sheared pin is an indicator that there is a problem somewhere, probably in one or more of the areas listed above.
A sheared pin, if retained is not a big problem in itself as the shaft can't really move far and has no inclination to do so ( not 100% sure on that, but it sounds reasonable).
So retaining the pin if it does break at least stops an annoying squeak or ticking noise, and would save an axle teardown to fix it.
I reiterate, though, the pins only break if the splines are worn or there is a misalignment problem. Normally the latter will cause the former.
Alignment issues should not occur in stock applications. There are techniques that can be used to check alignment if modified parts are being used. I covered the alignment procedure in one of my 32 sedan build videos.
Mart.