Death of a character in the Baratie arc
Gin hasn't been mentioned or referenced in the story since he left, so his fate his unknown at the moment, and only speculation can be used.

On the one hand, he did breathe in a supposedly lethal amount of poisonous gases, and may not have much longer left to live, as he noted himself. But on the other hand, several characters in the series have been shown to survive supposedly lethal injuries, albeit sometimes thanks to outside help. Pell survived the explosion from Crocodile's bomb in the Alabasta arc, and Luffy survived Magellan's poisons thanks to Ivankov's treatments and his own willpower.

Until Gin reappears in person, is mentioned by another character, or Oda clarifies the situation in an SBS, Gin's fate will remain ambiguous.