Old Biscuit, thank you for the link. It shows how to get the door back on to the roller. Unfortunately, it doesn't show how to get the roller back in the track, which I must do before I can put the door back on.
Heaterswa, how do you get the roller back into the rail from the back end of the rail? That end is deep in the pocket, and my hand/arm doesn't fit in the pocket opening, at least not that far into it. Also, how does loosening the rail from the ceiling help? And are you unscrewing from an angle since the door still is connected at the front roller?
Thank you both for your responses!