I highly doubt it ! They've been coming here for thousands of years and I'm sure many species still live !
If extra terrestrials ever existed are they extinct now?
They are extraterrestrial, meaning not of this planet. They are on their own planet safe and sound.
Depends on the age or stability of their system . . . Might have been some that died when a star went supernova near by . . . This IS what Kirk and crew are supposed to find out in their five year mission . . .