Thanks for the comments on investigating the curse. I have a group that really likes to be prepared, but I agree that having them discover a lot of this through play would lead to the best overall experience. I'll be sure to refer them back to the poem. I was thinking about letting them know some of the history that led to Kazavon's death, but I'm thinking better of it now. It's long forgotten knowledge at thin point, as far as I'm concerned. After all, the Shoanti barely knew anything about him in the previous chapter and they were the keepers of this knowledge. I'll also make some allusions to the infusion abilities they received at the end of the last chapter. They are getting undead-bane weapons or ghost touch armor and one free death save for a reason; there will be a lot of undead, incorporeal and death effects.
*MY* personal take is that healing spells that impart negative levels (Breath of Life, Raise Dead, and so forth) cause those negative levels because they're forcing a departing soul back into the body. Thus, if Bob the Barbarian went to -25 hit points and was "dead", he'd have to make the save against soultrapping immediately, and only if he saved would Breath of Life work on him. But yes, once he SUCCEEDS on the save, Breath of Life works, no problem.
This was going to be my take, too. As long as the spirit made the soultrapping save, they'd be able to be revived with Breath of Life or Raise Dead.