How about this for a darker ending.....
Whatever you do in the lead up, consider this as an alternate ending.
The planet that the DS is orbiting in ROTJ is Kashyyk. The rebel fortress is there. No ewoks, just wookiees (as GL first supposedly envisioned). All ground battle scenes that dont have ewoks (if possible) are spliced with the Kashyyk scenes from ROTS - obviously you cant use yoda etc. Han, Leia and Chewie are down there, trying to destroy the communications satellite dish that will lead the empires ground forces to the rebel fortress and kill the rebellion and all good and right people in the galaxy. Which becomes moot when......
When Luke is on the DS, and Palpatine says "Now witness the firepower of this fully armed and operational Battle Station!".....they fire and BOOOOOM! The planet below is destroyed! Cut to Nien-numb's shocked face, and Ackbar's falling into his chair, sinking his head. Luke grabs his saber after ages of inner conflict and whining and tries to cut the Emperor in two, now he's got a proper motive, and leading into the final fight. (Palpatine's just destroyed Luke's friends, sister, and also wiped out an entire legion of His own ground troops. The Greater Good, and all that. But I digress.)
When Luke's about to finish vader and turn to the dark side, you could intercut it with the scene from ROTS with anakin. Top-notch editing and some clever timing could intercut the two scenes very well, even coinciding the fall of Mace Windu with the fall of palpatine. All hell breaks loose in space, one of the DS lasers destroys Home One, the battle rages, culminating eventually in the fortuitous destruction of the DS. One-all. But the empire's fleet and the rebels are massively depleted. And, crucially, Han, Leia, Chewie are all dead, and the droids are vaporised.
With most of the rest of the rebels dead, luke still escapes the DS with Vader's body, returns to Tatooine, holds the lone Jedi funeral. The force ghosts of Ben, Yoda, and Anakin appear. Maybe include a shot of the Falcon returning to Bespin. Fade out on Luke looking at the (solemn, not smiling) Ghosts and beyond, to the twin suns?
Interesting idea that only really came to me this evening, and it would be a true darker end to the saga.
