What do you see in the above simulated collision between Andromeda and Milky Way?
Do you see any star smashing into each other? No.
Do you see explosions or physical carnage at the level of individual stars? No.
But, Do you see stars getting flung out? Yes.
See, galactic collisions are galactic level gravitational events, instead of stellar collisions. So mostly stars do not collide (because of unimaginable space in between), but they surely get gravitationally influenced.
If a star could come near to the Sun by around 50,000 AU, it will start flexing its gravitational muscle on. Things would get serious when a star comes closer than 1,000 AU (although very unlikely, but surely possible). That’s when things start to make a carnage a solar system level.
Some so much so that some planets will flung out of galaxy. (Notice how blue object gets effected by other gravitational bodies)
But which ones will be effected, or whether they will be can not be predicted because Galactic collisions are utterly complex processes.
Unimaginable number of highspeed astronautical dynamics can bring on any new threat at any time to the people living in the galaxies (assuming if there are beyond Earth). And by ‘any time’ I don’t mean in matter of days or weeks, but sometimes centuries and millenniums also.
Our Earth has faced a few violent phases in last 4.5 Billions Years. But most of time, it has stayed calm which has given life many chances to evolve. During collisions, this won’t change much, but the number and duration of calm phases are expected to reduce.
What do we mean by calm phase?
Something closer to what we see today, only a beautiful sky.
What do we mean by violent phase?
Quite Possibly .
Earth being flung out would be less likely though, unless extremely unlucky.
But while thinking about this and discussing this, we mostly forget one important part.
Any possible life, (if there would be) may have shifted to further planets because of increased Solar activity (as sun would also be about to die by that time around.)
Secondly, life would have evolved a great deal by that time. May be it would have started multiple times over by then, so somewhere else in the galaxy or in another galaxy altogether.
We humans take pride in calling ourselves intelligent in mere few 100 thousands years of evolution. By the time this collision would unfold, 3Bn + years would pass on.