It can cause.. 1. Runaway destruction of both the galaxies. 2. A new bigger galaxy formation. Is there any observations of solar systems colliding in our Galaxy? Is it a possibility, kind of precursor to when Andromeda approaches us and starts pulverizing our Galaxy. We shd experience heavy movement in outer zone of our Galaxy (due to Andromeda's Gravity) even before Andromeda hits us, kind of triggering mass destruction for both the galaxies. Or both the galaxies will hug or permeate peacefully due to very large spacings between stars and settle down as a bigger galaxy.