You may be familiar with this one. It was adapted for television (Twilight Zone, if I'm not mistaken), and the teleplay was quite good as I recall. I believe James Whitmore played the lead and he acted up quite a storm.

Hawksbill Station is a time in earth's distant past to which political prisoners are exiled by time machine. It's a one-way trip, it is physically impossible for them to go home. The atmosphere is breathable, but there is nothing there but desolate wasteland. The only form of life is one-celled microbes, pond scum and ocean plankton.

The prisoners are sent back with a few tools and agricultural equipment and are expected to make out as best they can. Cut off from the society they knew, perhaps where fighting for, despair and madness stalk the colony. Only one man holds it together, for decades, by sheer force of will. His leadership keeps the group together, gives them the will to live, keeps them organized and working at the tough job of surviving in the unforgiving landscape. He is a tough, but fair, leader, and even those who oppose him give him credit for the work he has done keeping them alive.

Well, I know you'll see this coming. Eventually, the dictatorship far in their future is overthrown, and science develops a method to not only send a rescue mission, but they have the technical abilty to bring the exiles home. They have been pardoned of their crimes and are welcomed back to humanity and their own time.

Suddenly, our hero finds himself a man without a mission. Everyone is consumed, even obsessed by the idea of going home. The crew sent to rescue them become demi-gods, celebrities. They are decent men, but all they are interested in is packing everybody up and making the elaborate technical arrangements to send the convicts back. The colony leader begins losing his grip on the Station. No one wants to work, to maintain their equipment or do the chores. His authority starts to crumble, and his very reason for existence is quickly becoming obsolete. When he goes home, he will no longer be the savior of his people, he will be just another returnee.

It pushes the man over the edge, and most of the story chronicles the psychological collapse of a strong and dedicated man whose very reason for existence has suddenly been taken away from him. I believe this was Silverberg's first work, and if I'm not mistaken, won him a Hugo or Nebula award. Not a bad start to a great career.