You are in a desert hundreds of miles from civilization including any roads. All your forms of communication and gear are on the truck that you are driving. you are outside of your truck looking at something and someone gets in your truck and steels it.
Assuming that you did not set up with a person to check in with every night so that no-one is expecting to hear from you for several days. This now places you in a position where it would be impossible to walk to safety and live nor is someone going to come and rescue you unless it is by chance.
Would one be justified in shooting the person steeling your truck as it is that action that will eventually cause you to die of dehydration.