Oh wow! What is it that makes you think they'd be dead in 24hrs? Just from inexperience or..? I've no doubt that some cats maybe prefer their creature comforts to the opportunity to go outside! In the case of my Jasper, the lady I rehomed him from when he was about 10 months old, told me categorically that he's not a fan of going outside at all. But he really is! He makes that loud demanding MEOW when I lock the cat flap for whatever reason. He really likes to go and explore. But then my kitten Fiona, she's happy to go out into the back garden, sit on top the she'd and watch the world go by. She never really goes far. But I don't live on a busy road and it's fields for miles out the back of my house. So it's pretty much as safe as it can be I suppose! No farms nearby with grumpy farmers either!