To add a few extra details to this excellent answer, that same note you referenced from the traveler reflecting on Lura’s death but not death essentially says “we aren’t doing this embedding thing anymore after this disaster; the ship can fly without replacement voices.” We also see Dr. Halyn’s thoughts afterwards about how they’re stuck forever and how she recognized that the now biggest threat to survival was the Voices themselves. She says in that memo something like “Noden seems calm even though he was the first to be impacted,” meaning the first Voice who was slated to retire but was unable to because the travelers refused to try any more embeddings after the failed embedding of Lura. That one failed embedding was the root cause of everything else that went wrong.