Even if your yard is depleted of N, that is not the most important element in the fertilizer needed for a new lawn. While you will still some Nitrogen the thing your
seed will need most is the Phosphorus. That is the 2nd number on a bag of fert. The best starter fert is something in the range of 18-24-12 with at least half of the N being slow release.
Now are you certain that the lawn is dead? Fescue even though it is drought and heat tolerant will go into dormancy and look dead during times of high stress. If this is the case watering will help bring it back.
It is always best to use a mixture of different types of
seed in your lawn. Having only one type can lead to problems, since if a disease that attacks fescue hits your lawn you would have nothing else to fall back on, where if you had a mixture of fescues rye's and blue grasses the damage would not be as sever.
I hope this helps you out!
Mike Maier