Could thermal loss or ingestion of too much salt water cause delirium in such a short time?
Paradoxical undressing is when the person removes warm clothing while in a state of hypothermia, which further increases heat loss. Because they are suffering from the cold and their body temperature is below the safe threshold, it seems incongruous that they would be removing warm clothing and causing themselves to become even colder.
To be sure, the phenomenon of paradoxical undressing is an enigma counter to expected behavior. With their core temperature below 90 degrees F, hypothermia sufferers frequently undress themselves. Urban victims of hypothermia that are found in a state of undress are often thought to be victims of assault.
http://www.survivaltopics.com/survival/paradoxical-undressing/
Yep, as a kid I got caught out in the cold and had decent clothes on for the weather but got wet when I fell through ice in a shallow creek and in just fours hours was loony toons. My friends got me to shelter and I was mumbling and ranting till they got me warmed up.
I was shivering so hard I was barely able to walk with help (Two guys on either side of me) after a few short minutes of being wet in Zero Degree weather.
Hypothermia, ingesting salt water, and the stress of the situation does lead to loss of judgment, delirium and hallucinations which led to their giving up, or thinking that they might be able to swim to land, a boat, a light, etc. That description is typical for someone stranded in cold ocean waters for a long time; but less than 40 hours does seem a bit too short. I think they were just not mentally tough enough to get through it, but they could have if they stayed calm, stayed together and supported each other, and had their wits about them, knowing that a search and rescue would be sent for them.
Sad.