Will the astronauts in Artemis II not all make it back alive? 

This market resolves YES if any of the four Artemis II astronauts die during the mission. This includes deaths occurring at any point during the mission: launch, transit, lunar flyby, return, or recovery operations. The market resolves NO if all four crew members (Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen) return alive.

Resolution will be determined by official NASA statements and credible news reporting of the mission outcome. See 

Artemis II will carry NASA astronauts Reid Wiseman, Victor Glover, and Christina Koch, along with Jeremy Hansen of the Canadian Space Agency, on a free-return trajectory around the Moon and back to Earth. Launch is scheduled for no earlier than February 6, 2026. Artemis II builds on the success of the uncrewed Artemis I in 2022, and will demonstrate a broad range of capabilities needed on deep space missions. The spacecraft will circumnavigate the moon on a slingshot trajectory designed to bring the astronauts back toward Earth — even if something goes wrong and the capsule's propulsion system fails.

At lunar distances, the astronauts will face a far harsher radiation environment than do the vast majority of space travelers, as astronauts on the International Space Station are still "within the protective envelope that helps shield us from some of that space weather." Additionally, the schedule was delayed due to investigations into issues with Orion's life support system and unexpected damage to Orion's heat shield observed after the Artemis I reentry.