Maths Homework?

I presume that you are asking for the probability that tomorrow (say) everyone in the world dies except you.

Assume that the average person lives 50 years = 18,250 days. If there is a constant risk of death this is a probability of 1/18250 = 5.5x10^-5 per day. There are 7.4 billion people on Earth. The probability that you survive tomorrow is 18249/18250, which is very close to 1. The probability that you survive but everyone else dies is approx. 1*(5.5x10^-5)^7.4x10^9. That probability is so small that your calculator cannot display it. Expressed in terms of odds, it is 1 chance in a number which is many orders of magnitude larger than the number of atoms in the universe. The probability is so small that it is meaningless. Even if the human race survived for as long as the universe has already existed, there would still not be any significant chance of such an event happening.

One hiccup from our sun, or a blast of radiation from a pulsar, the sun expanding, a large meteor hitting earth, etc, etc., and everyone on earth dies. Our universe is a dangerous place.

When everyone dies, there is always a last person. So the chance of a last person sometime is 100%.

100%. Some day our planet will die, and so will the people. There has to be a last person to die.