For now, humans have no way to fly out of the galaxy. The milky way is just one of the hundreds of billions of galaxies in the universe, in the past, we thought that the diameter of the milky way was 100,000 light years, but the latest scientific research show that the diameter of the milky way was increase two times larger likely 200,000 light years. If the level of the human science and technology can not be developed by leaps and bounds, at the speed of current technological development, it is impossible for humans to fly out of the galaxy after 100 million years.
Beside once flying at the galaxies extremely dangerous. Beyond the milky way is an extremely empty deep space of the universe. It may be have an atom of hundreds of thousands cubic kilometers. Without star and other intersetellar matters, it provides energy suppliments for spacecraft, while atleast millions of light years are reached from the other milky ways, remote. If the spacecraft really flies out of the galaxy, it means eternal loneliness,and soon the energy will be exhausted, and the living system will not guarantee that life will survive so long. Therefore flying out of the galaxy does not make sense at all.
According to the assumption of the alien civilization level pruposed by the former Soviet Astronomer Nicola Caldasher in 1964, assuming that there is an Extraterrestrial civilization. There is a three level of civilization
*Star rating, such an energy that can domimate the entire planet and the moon
*Constant star rasing, can dominate the energy to the entire solar system. ( 30 to 100 billion times that the level 1)
*At the galaxy level, the enerygy of the entire milky way can be utilized. (1 trillion times tham the second level)
If the civilization wants to communicate with the outside world, it needs a lot of energy.
The level is low, although it can fly out but it is difficult to come back when flying out. So there is no need.
When we think about how big the universe it, and the possibility of us being alone in it, it kind of scares us.