Actually, Palpy does return and brings Luke over to the Dark Side.
The films aren't bound by that history, well-written though it is.
Perhaps 7 will be "The New Republic" covering
Bacta War/Thrawn Crisis and 8 will be Dark Empire story about Palpy's
return and 9 will be about the Yuuzhan Vong invasion/liberation.
Not a chance. There's no way Lucasfilm would ever film the novels. If, by
some chance, we ever get 7-9, they'll certainly be new stories.
7: Luke is elected Chancellor of new Republic and restores Jedi
Council. His search for Jedis turns up Lando's son, Renio Calrissian
who's mother is Mace Windu's cuz. Han and Leia have 2 sons with the
force, she also fends off a Tatooine assassination attempt for killing
Jabba on Corellia. Luke gives up the Chancellor position to second in
command Lando who is more of the politician anyway. Luke is then able
to focus better on the growing new threats to the republic including
some who were Empire Loyalists. They foil a plan to blow up Coruscant
and conduct a super fast hyperspace chase. Yoda's ghost makes a
reappearance and teaches Luke how to sacrifice himself should he need
to by melding himself with the force by summoning all the powers of the
force inward.
8: Her sons grow in the force, Cain and Abel story. The sith's first
dark deed is to kill his brother. Now it's Luke, Han, Leia and a
fledgling troop of jedi vs a very dark Sith Knight. The Sith Knight is
almost caught but escapes and recruits a great force of discontents
with the New Republic.
9: Major attack on capital targets by Sith, Republic almost overthrown.
Deadly virus that kills slowly while also affecting midichlorians makes
Jedi's go crazy/insane while making their Jedi powers erratic. Dark
Troops and new major weapon that can destroy galaxy also threaten
safety. The Sith has recruited improved troopers with the virus that
gives them power (like a steroid) but shortens their life spans. The
Jedi are weak and it is up to one brave