As we do in real world too. The character lifespan is about 500-600 hours, though some live shorter or longer lives than that. My first char lived to age death, as I played him 627 hours, though he would have lived longer than that, but I accidentally worn a certain age + item, which killed him for good. Old age, which I reached approximately at 460 hours, reduced strength, dexterity and constitution. If you save practices to old age, you can compensate this negative effect. You will have one RL hour to say goodbyes to your IC friends after dying to old age. In my case, I played that character for ten RL months. I think this time is enough to play the one and same character.

The other way to die permanently is con loss. When you die IC, your constitution will be reduced by 1/3 of a point. So, after three deaths you lose one point of con. When your constitution is reduced to 3, you will die permanently. The characters that die to con loss are often suicidal or overly brave by nature, and thus die often. Con loss is seen as a death of a true warrior, and people tend to give their respect to the characters who sticked in there to con loss.

The most common way to die permanently in CF is character deletion, which means that you get tired of your character and delete him for some reason. Losing your character to age death or con loss isn't really something you should be worried about, as it is fairly rare insident, and others are likely to give you kudos for job well done in the cases you die by either of these ways.

Your work will not be wasted when the character dies, as you are probably a better player after playing that character, so you'll probably do better with your next character. And your character will still live in the memories of those who knew him.