@Varsuuvius @RRollplaying I'd also check out Eberron's Undying and Undying Court. The elves achieve a similar state as Lichdom except through positive energies instead of negative. D&D has precedent for good undead, undying creatures.
@JeremyECrawford , if a spellcaster fails their Arcana check using a Mizzium Apparatus and a new spell is cast instead, does the spellcaster get to choose new targets for the new spell and could they apply features like Sculpt Spell and/or Metamagic options? Thanks in advance!