The point of this text is not to predict how many people will ever live. What I learned from writing this post is that our future is potentially very, very big.
If we keep each other safe – and protect ourselves from the risks that nature and we ourselves pose – we are only at the beginning of human history.
The fact that our actions have an impact on the large number of people who will live after us should matter for how we think about our own lives. Those who ask themselves what they can do to act responsibly towards those who will live in the future call themselves 'longtermists'. Longtermism is the ethical view that we should act in ways that reduce the risks that endanger our future, and in ways that make the long-term future go well. 1
It is not possible to answer this question precisely, but demographers Toshiko Kaneda and Carl Haub have tackled the question using the historical knowledge that we do have.