Please read this: http://www.care2.com/causes/kitty-marooned-on-a-roof-is-finally-rescued-after-two-months.html
The moral of the story:
If a cat is stuck for too long in an inconvenient spot, it will have no access to food or water. Dehydration and starvation will set in quickly.
You may decide to give a cat the chance to come back down on its own. If that’s the plan, never leave a cat which seems to be stuck for longer than a day or two at the very most. If it isn’t down by then, it needs help.
If you’re dealing with a declawed cat or one that isn’t ordinarily outdoors much, you’ll probably know pretty quickly if it can’t get down. Find help as soon as you can.
The moral of this story is to keep a watchful eye out for animals in distress. Don’t assume they have a natural ability to get themselves out of jams. Don’t feel confident someone else will take care of it. Make the call for help yourself and watch to ensure the situation is appropriately resolved, because every so often our animal friends need a gentle helping hand from us. Be alert enough to realize when that situation is playing out right in front of you.