The scarf joint for a peghead/neck relationship is a technique stringed instrument builders have been using for hundreds of years - it gives more strength than no joint or a butt joint, the glue is stronger than the wood. Because the nut is the weakest part of the instrument, it's almost a guarantee that if the guitar is around long enough, it will get broken here (every Strad has a new headstock). The point is you want to make an instrument that is WORTH repairing. If you build with this in mind, then even splicing an entirely new peghead on isn't even crazy expensive, though usually they break in a way that we can keep the original peghead. We can sometimes make an entirely invisible repair, but that also requires a complete refinish. In any event the repair is invisible to the touch, and it won't break in the same place again.
I think that the early Alembic instruments suffered more breakage because of the bridge placement, the peghead is out a little farther, and wound of up hitting things more frequently since players weren't accustomed to the extra reach. Usually a repaired peghead from the 70s will have a good chip or chunk on the back of the peghead as well, point of impact. Some are from stage/stand falls, but most seemed to be whacked on something.
