So we don't have to worry about the sun going nova in 5 billion years? Hmmmm.
Something don't compute right here.
It might be best for you to think of a galaxy as a gas that has no internal pressure that is held together by gravity. When another gas of the same type tries to pass through, it is not necessarily going to cause collisions (because that would imply that either gas had an internal pressure). It will, however, alter the gravitational forces that control these galaxies. Stars will move in different paths, and in certain areas the density of the stars will increase or decrease. It is unlikely that our Sun will be physically battered. It will more likely follow a slightly different path each time it orbits our galaxy. Since it is estimated that our Sun takes about 250 million years to complete an orbit, and this galactic collision which will occur in about 3 billion years will probably take about a billion years from beginning to end, the big question is where our Sun will end up once it is done. Will we be citizens of the Milky Way Galaxy? Will we have a lot more or a lot less stars nearby?