As the are letting all the air out he hops up out of his cot and saves
the day by pressing a switch that the creature is blocking or something
but the film is very dark at this point and we don't see what happens to make him die like he does. I have always even from childhood been confused on this issue.
Did the ship's captain, Col. Van Heusen, die?
I saw the movie a long time ago and again on Feb. 5, 2022 on Svengoole.
The spokesman at the end said that only 6 out of the first 19 people on Mars survived. The first expedition had 10 crew, the 2nd had 9 (deliberately leaving some room on the ship for possible survivors of the first expedition?).
With Carruthers from the first expedition, there were 10 people on the ship on the return voyage. And I hope that they wouldn't have had to leave any additional survivors behind on Mars, but instad had room and supplies to take all 10 back to Earth if they were found alive.
I wasn't certain who lived and who died so I checked the cast list.
Col. Carruthers, protagonist, 1st survivor.
Kim Anderson, protagonist's love interest, 2nd survivor.
Joe Keinholz 1st victim.
Gino Finelli 2nd victim.
Bob Finelli 3rd Victem.
Mary Royce 3rd survivor.
Eric Royce 4th survivor.
That leaves 3 men with two survivors and one victim among them.
Lt. James Calder.
Major John Perdue.
Colonel Van Heusen.
One ot them, not the colonel, was wounded in the head by the alien but was in the group of spacesuited survivors, though he might have died later from the effects of his alien wound.
One of them, not the colonel, wore a spacesuit and was trapped in the lower levels by the alien, using a blowtorch to fend it off. His helmet was ripped up, but when the alien headed for the upper levels he was told to hop for the airlock on the lower level. So he might have suvived letting all the air out of the ship. Or he might have died.
Colonel Van Heusen was wounded in the leg by the creature and was very sick, apapently with lukemia. He seemed to think that he was doomed. He fell down in the final confrontation with the alien but I didn't notice anything that might have killed him. He might have died then, he might have survived to die from his wound, he might have made it back to Earth and been curied.
On balance, it seems like Colonel Van Husen was the one who died somehow in the final confrontation with the alien, sacrificing his life to let the air out of the ship. After all, he was the former love interest of the protagonit's new love interest so him dying would be a normal movie cliche.