That would depend upon a number of factors. How serious is the person's illness? Does he have medical care? Does he have sufficient water and food and shelter? If the person does not have a life threatening illness and is living in a town or city in the desert with water and food, that person can survive indefinitely. Thousands upon thousands of people are in that situation everyday.
With sufficient nutritious food and plenty of water, a person can survive indefinitely.
With sufficient water and food a person could survive indefinitely. Without water, just 2-3 days in the summer months.
A person can survive indefinitely if that person has sufficient food and water.
Very hard. Without water, a person will not last long. It takes a specialized form of life to survive in the little/no water dessert. People can die in a desert very quickly without enough water to live.
A Long Time
They can survive indefinitely as long as the food is nutritious and they have plenty of water.
Abyssinian cats are a domestic breed and would not survive for long in a desert.
Not for very long. People cannot survive for very long without water, anywhere.
What are the conditions? If it is during the hot time of the year and you have no water, you will be lucky to survive more than two days. If you have sufficient water and food and have shelter from the sun you can survive indefinitely.
3 days if he/she doesn't have water and food.
Cattle are allowed to graze in both cold and hot deserts, at least in the United States. However, they are not natives to the desert but domestic animals. They could not survive long in a desert without human intervention. Man provides them with a water source - a pond or a stock tank that is often kept filled by a windmill.
As long as a person has proper clothing and sufficient water, a person can remain outside in a desert biome indefinitely.