Die in a week.
The problem with living forever isn't even when humanity dies out, the older you get the faster the years go because it represents a smaller and smaller proportion of your life - by the time you're 500 years would be gone in the blink of an eye. You wouldn't be able to form meaningful relationships as you'd have nothing in common with the people of the day, with no interest in their pop culture (what do your grandparents think of your fave and of current TV programming? Have they even learned how to use modern technology?)... You'd be sitting alone in a retirement home or research facility doing nothing.
Immortality would be the worst. You'd lose touch with reality pretty quickly. By the time the world ended you probably wouldn't even notice or care about the difference.
