The interstellar medium is less dense outside of galaxies, but it's already very sparse and it doesn't do much. It makes no difference to a star system that might be outside of a galaxy.

A star would have to make a near pass with a black hole or a neutron star to be slingshot into relativistic speeds, which almost certainly would not happen to a single star in a galaxy collision, statistically speaking. A star does not need to travel nearly the speed of light to escape a galaxy, but stars also almost never escape anyway because galactic collisions are so rare and are one of the few events capable of doing it. More likely, a star that escapes a galaxy is somewhere in a tail of matter being pulled away slowly from its home galaxy via a collision like pictured in the post, in a small chunk that the galaxy's gravity never recaptures.

Right, almost no matter at all collides. The biggest change any star system may find is being ejected from its galaxy, but everything inside the star system keeps orbiting as normal, the planets around the star don't mind. Star formation may be invigorated by colliding and collapsing dust clouds. If life exists on a planet in a colliding galaxy, the other galaxy looming large in the sky would make observation and science virtually impossible for any part of space behind it.

Unfortunately, manufacturing hundreds of millions of personal electric vehicles is not going to get us any closer to zero emissions, that's a car industry marketing ploy as pervasive as the recycling symbol on plastic bottles. Emissions will still come from mining the resources, manufacturing the cars, continuing to build highways to support them, and doing all of it more and more for the ever increasing number of cars on the road, continuing to clog them and make travel times longer in cities. Only building out public transportation infrastructure at a ludicrous pace can possibly lower our transportation emissions. Until you see that happening; train lines and bus lines and dedicated bike lanes being built like there's no tomorrow, the halting of new highway construction; we're still at business as usual.