Nightmare

Based on the fact Ishar can take a bond from someone as he almost did with Dalinar and The Stormfather’s bond, could he take a broken bond such as the one between a “dead” spren like Maya and transfer it to a new person, such as Adolin, to have them swear a radiant ideal to revive the spren by having the same bond attached switched to someone who hadn’t broken their oaths. It may be less satisfying than what Adolin appears to be on the path to accomplishing, but it’d be a way to bring back all of the dead-eyes.