What will happen to bitcoin if the world population increases?
The amount of bitcion in circulation does not increase or decrease based on human population.  So, yes, it will likely be distributed more sparsely among people if the world's population increases.

However, bitcoin is only divisible to 8 decimal places, and your example uses 10.  It's also difficult to say what role Bitcoin will play as far as global currencies go, so it is unwise to assume that an amount as small as 0.00000001 will be equivalent to a modern day yearly salary (or whether Bitcoin will be used for salaries at all).  Speculation like that is off topic in this forum, which is why you've received some close votes.