In bay lore, The excuse for disconnecting is "Space Sleep Disorder". There is another condition, a subcondition based off this, "Rapid onset space sleep disorder". I think that examing someone that disconnected should let you differentiate. Scan all radio chatter and local "Say" chat for any mention of the term "SSD", and if they disconnect within 10 minutes of saying "SSD", the examine verb will say "[user] has succumbed to the effects of space sleep disorder", but if they just disconnect, leave it as is with "They have suddenly fallen asleep!".