IANAP, but what I'm seeing here is a lot of very optimistic speculation about how life might survive, with no plausible mechanism. We have no idea what dark energy is, and it may well be impossible to extract energy from. Some of the quotes in the article suggest that life must physically go find additional energy sources, especially if dark energy doesn't work out. Interstellar travel is already prohibitively difficult, and getting to the next galaxy seems simply infeasible. Humanity's descendants are basically limited to the Milky Ways resources. Left to itself, the universe will eventually run out of hydrogen that can be economically fused. It will go dark eventually. The black hole power plants will eventually run out.

Wake me up when dark energy is more than a statistical anomaly, or we have a practical theory for a warp drive.