I was operating on the assumption that horcruxes were supposed to make one nigh invulnerable, like the soul-displacement objects of myth by which they were inspired, with the unstoppable killing curse being an exception. Being left as a disembodied shade after death would be a side effect rather than the main purpose, so the body returning spell would not be a necessary complement. It made sense in light of what I thought horcruxes were actually for.

Apparently the conversation between Tom Riddle and Professor Slughorn in Half Blood Prince contradicts this, but I had forgotten it.