Matt O'Dowd from the web series PBS Space Time gives a 30 minute presentation on the possibility of escaping the Long, Slow Decline and building a galactic civilisation. The problems facing us are lack of drive, the energy cliff, and most importantly the ability to communicate.
His conclusion? If the speed of light is the absolute limit to communication then it should only be possible to sustain a civilisation over a few hundred light years before distances become too great and fragmentation occurs. The galaxy may be full of civilisation, but they are too far spread out to effectively communicate with one another.