Removing inflict/harm is the simplest way to balance out giving Dark Apostate identical self healing as a Pale Master, but you could also leave it there and disable the ability for harm/inflict to target self if you're in the Dark Apostate's shadow form, which I imagine would be a more complicated change for SSG to make. There's already a death domain, but yes it would make more sense to take that over and redo it while the new evil domain parallels the alignment based good domain. You'd drop the tier 5 harm improvement enhancements and replace that with something more connected to curses and/or offensive debuffing, I proposed an idea above and other people have suggested other good curse/debuff based ideas too.
I agree, if it were me I wouldn't add or change anything related to negative based self healing beyond what Lynnabel already has designed. As it is now, you'll be able to play an undead Wizard that heals with multiple auras and one other spell, an undead Warlock that heals with one aura and one enhancement under a layer of temp hp, or as an undead Cleric that heals with multiple spells and one enhancement as well as being able to cure afflictions that aren't already prevented by the form. To me that is building up a variety of reasonably balanced and survivable builds that anyone can choose from who likes the idea of playing an undead form.
But people are arguing that the potential self healing capabilities that an undead form cleric has are inadequate so this is mostly just an exercise in trying to see what amount of additional self healing capability would satisfy. It's been further argued that what it definitely needs is some kind of healing over time, either a long running passive aura or a short term dot like Vigor. It's a thought exercise - would people be happy to trade the self healing that an undead cleric already has (the inflict/harm line, and let's also, for the sake of completeness, turn off the penalized self healing an undead cleric could get from their own heal spell too) for the combination of Death Aura and Negative Energy Burst? Or if the healing portion of Dark Consumption was turned into a negative energy clone of Vigor, is that enough healing capability?
I'd also like to figure out why the argument that Dark Apostate requires a healing aura doesn't also apply to a Divine Disciple or Angel of Vengeance? Going tier 5 in those offensive nuke trees locks you out of the heals over time available in t5 Radiant Servant and t5 Beacon of Hope. But I don't see a lot of forum complaints that, sure, Favored Souls can self cast heal and cures on demand but they still definitely need a healing aura or Vigor spell to make them adequately capable of healing themselves...
Let me admit this though - if everyone here can successfully cajole SSG to not only open up the possibility of a pure class undead form cleric, but throw in Death Aura on top of that, I'll play that build into the ground with great joy even if it is absurdly unbalanced (or rather, because it is absurdly unbalanced).