Challenge of the week: survival analysis

Let's say that the average lifespan of a human being is L 70 years. The probability of dying this year, at any given age y, is p(y). Let's assume that the number of people that are y years old is M(y), and that p(y) is a monotonic decreasing function of age. If we have 7 billion human beings on Earth today, given these assumptions, how many will die this year? Now the question is: what is the lower and upper bounds for N (number of people who will die this year), regardless of the functions M() and p(), provided p() is monotonic decreasing, and that average age at death is L 70 years.