And there’s another theory tangential to it all. I think this could all be a test to recruit Ichigo. The cuts to his training all point to an emotional conditioning for bloodthirsty combat; that kind of initiation would explain all the bad attitudes among Reapers. But this is a debate for another time.

We know from…Hanaku? The squad 4 guy and Rukia that Soul Reapers know crap about human society. This suggests that, if they did use to be human, it was so very long ago that the human world is alien to them. Yet the “soul candy” pez dispenser and that one clown of a Reaper back in the Grand Fisher episodes suggest that some Reapers are actually in touch with the right century. And so a key question to the nature of Reapers — their humanity — is up for grabs.

If we assume that they were once human, then they will be reborn into the human world, for this preserves the balance. Death is as permanent for them as for anyone, but their perspective allows them to see resurrection and rebirth as a continuance of life rather than a new start entirely.
If we assume that they were not, then we got nothing. A creature outside the definition of alive cannot end life in death, but it might still be possible to end that existance in an approximation of death.

However this doesn’t seem heroic or as ’shocking’ a development as they might want to pull on the audience.