If you do not repent, you will all perish as those Galileans did. Those who reported to Jesus about the slaying of the Galileans by Pilate must have regretted their decision. While we cannot know what kind of response they expected to get from Jesus, we can be sure that the one they got was far from what they would have expected. It was a sad fate that befell the slain Galileans, and Jesus seized the opportunity to warn those who were listening to him to take care lest they face a fate worse than that of the slain Galileans.
Those who were reported to have perished were victims of what we can today call political massacre (they probably were revolutionists who were rising in arms against Roman occupation of their land). It was not because of what they did or failed to do that led to their untimely and unnatural demise. And Jesus made this very clear to those who came to inform him of the news, as well as to those who were listening. However, Jesus took the opportunity to bring to their attention the presence of a punishment that is much worse that the one meted out by Pilate: being sent away from God’s presence. It is a fate that, unlike the “accidental” massacre perpetrated by Pilate on the unfortunate Galileans, is sure to come unless one leads a life that prepares him/her to meet God (a life of repentance). 
Jesus proposes repentance as the only way of ensuring that one escapes a fate that is worse than being sacrificed. Repentance is all about living a life that is in conformity with the values of the kingdom. It is about attuning one’s life with Gospel values, living a life that is true to one’s essence. Those who refuse to leave behind a life that estranges oneself from God are sure to meet such a fate. It will be one’s fault if such a fate befalls him/her since we have been given Jesus to teach and show us how to get re-united with the Father.