Aren't chicken pox fatal...? 
In a very few cases, yes, it is fatal (you're probably thinking of smallpox, you know, we gave it to some of the natives...). That's actually why the vaccine was developed; most people view it as a normal part of childhood, but since it is occasionally fatal, there is a logic to using the vaccine. However, there is some question about whether the vaccine gives you life long immunity like having the disease does, so there are some reccomendations about boosters for the vaccine.
We didn't have to think about the vaccine; the year our oldest daughter was in kindergarten, she broke out with chicken pox on Christmas Day, and her younger sister followed a week later. Just in time to return to the babysitter, as we had to go back to work. We actually called the sitter, to see what she wanted to do (if she would allow a child with chicken pox to come to her place); she polled the other parents involved, and it turns out there was a waiting list of kids that the parents WANTED exposed, so they could get it over with...apparently, it's not uncommon to have "chicken pox parties", where, if one kid gets it, all kinds of kids come over to visit and play, hoping they'll all get it and get it over with.
