As Mark marched through the desert, the high winds blew sand at speeds that stung his exposed skin. He looked back and could see his footprints for hundreds of feet, beyond that the winds had blown them away. He had no idea how long or how far he had walked. He turned his back to the wind and opened his canteen. He attempted to pour it into his mouth, but there was not a drop. He rolled his tongue around the nozzle of the canteen, but it was bone dry. Mark dropped the canteen in the sand and continued walking. His steps slowed. He was getting dizzy. The sun's rays seemed to only increase in intensity throughout the day. It hung high overhead and punished all that resided in the desert beneath it. Mark was lightheaded. He felt his knees get wobbly ...

According to the passage, Mark is clearly lost in a desert. He has been walking for, most likely, a very long time under the scorching sun. He has no water to drink. At this point, we can already assume something bad will happen if he does not find any water to drink soon.

The passage goes on to tell us Mark is now slowing down. He is dizzy, lightheaded, and his legs are weak. These are clear signs of dehydration. The lack of water is affecting Mark's body. The next logical stage is fainting since his body does not have what it needs to keep on functioning.

Therefore, we can predict:

Mark will pass out due to dehydration.