Meh. At 15th level, that trick is already possible via Regeneration spell; and Lore Bards have been doing essentially the same thing to their allies since 6th level w/ Aura of Vitality. Variant humans may have been doing it since level 1 with the Healer feat.
You're still vulnerable to insta-death, and getting grappled/kidnapped by a dragon to kill in isolation (away from help, including the aura); you're still vulnerable to petrification from a Medusa, or brain-eating by an Intellect Devourer, or getting Plane Shifted by a Rakshasa to the Elemental Plane of Fire, or getting shredded by a horde of zombies who auto-crit you to death and then start eating you on the same turn you go down to zero HP.