Idk about you guys but when I think of a Necromancer healer, I think of an inverse to SCH.
There would be a corpse of some sort that follows the Necromancer around and they siphon the life forces of their "pet" to heal party members with. The corpse would have abilities like drain so that it would attack enemies to recover its own health so that the necro could continue to pilfer its health for the team. Ofc for this to ever work the pet would need substantial amounts of support to ever be viable and even then I can't imagine it going over well due to how clunky the current pet system is that it would be an outright nightmare to get functioning.