It occurred to me a few weeks ago that Psychohistory would be a way to give PCs a meaningful role through the Rebellion or Hard Times, which would address one of the major criticisms of those metaplots. They could be assigned missions intended to bend the curve of history: the Hard Times cannot be prevented, but PC actions could help reduce the length and severity of the turmoil.
The difficulty is showing or giving the PCs a sense they are making a difference beyond their psychohistorian boss telling them so. It is part of human psychology that prevented bad outcomes are harder to intuitively grasp than undoing bad outcomes that have already happened, hence why it is still so hard to get people to practice preventative medicine. If everything works out, nothing bad happens.
So PCs deliver critical life support parts or medicine to a dying world, that allows them to keep going for a few more months. Unless the PCs keep up the stream of deliveries and unless they are dealing with tiny populations it is difficult to see how they will make a long term difference beyond delaying the end. Maybe in that time, the dying world ships a bit more of its mineral output to an industrial world but again why would one more shipment make a lasting difference?
The way I see it, the PCs may postpone the death through a delivery, but then the harder task is setting up the business deals and logistics necessary to keep dying worlds from dying as soon as the PCs wander away.
Now a GM could be bleak and say that postponing the death of a world for a few more weeks or months so a few more people can get away is already a victory and bending history. Maybe but too many such bleak victories can be pretty draining for players and it may feel like their efforts are totally futile in the bigger scheme.