The air pressure in an aircraft(cabin pressure) is kept higher than the atmospheric pressure at high altitudes to avoid discomfort to passengers due to low outside air pressure. This process is called cabin pressurization. An increase in cabin altitude is actually a decrease in the cabin pressure.
temperature in the aircraft is internally controlled according to the temperature zones throught which the aircraft is flying.
planes are constructed in this way to ensure the comfort of the passengers flying.And if it is not constructed this way, planes won't be able to fly high and long.
there is a very less chance for these systems to fail. Just in case, if the cabin pressure fails we have oxygen masks. If the temperature controller fails, it is either going to be too hot or freezing cold.
I am not so sure if they have an alternate for temperature control.