Yes. Adding the option of managing sleep, hunger, thirst and temperature brings a huge dimension to the game. It shouldn't be mandatory, it should be optional though. My idea would be (since you don't have a pip-boy) to give you three options to choose from:
Normal Mode: Choosing in between no hardcoe and hardcoe at any time. When turned off and back on, your status remains where you left it when you turned it off.
hardcoe Survivor Mode: Hunger, Thirst, Temperature and Sleep are kept on at all times, death means you will lose your save file and be returned to the main menu.
Since you don't have a pip-boy to monitor your current status, I believe that a small message should appear at the top of your screen. Three warnings is enough, and it should be realistic. You shouldn't get the third warning until after a day of no progress with that certain issue. Also, the more the player does, the faster the bars move towards certain doom.
For example:
Hunger:
- Your stomach starts grumbling.
- You are hungry.
- You are starving.
- (Player dies from starvation)
Thirst:
- You feel thirsty.
- Your mouth is getting dry.
- You are dehydrating.
- (Players dies from dehydration)
Sleep:
- You're feeling drowsy.
- You are tired.
- You are exhausted.
- (Player goes unconscious for twelve hours)
- (If your player is in third level of starving/dehydrating when you fall unconscious, player dies)
Temperature (Cold):
- You're freezing.
- You can't feel your fingers.
- Your body is moving slower.
- (Player freezes to death)
Temperatue (Hot):
- You're feeling hot.
- You're getting very hot.
- Your blood is boiling.
- (Player dies from heat stroke)
- (The warm temperature should cause your thirst to go down faster as well)
These are just examples of something I'd like to see.