Anyone who has seen what happens when strong arm tyrannical regimes collapse would know that the story is far from over.
The PT would have us believe that the Old Republic was already in a state of corrupt stagnation and Palpatine exploited this to create the Empire.
With the Empire out of the way all those influences held down by the Empire would pop up and frustrate the former Rebels in the attempts to create a better society.
That may force them to consider strong arm tactics themselves and Leia would be the obvious next Skywalker open to temptation.
A political leader with a passionate temper and Force abilities seeing everything she has fought for under risk.
She seems like an obvious character to create conflict in, not Luke.
Potentially such a story would be much more interesting than Anakin's fall because we already care about her, that half of the equation has already been drawn.
The idea that ROTJ is the clear ending of the story shows an epic lack of imagination.