The Long Path (aka 'main path') is the true path (including full or most points) and true ending to King's Quest 6 and is thus the ending the original canon continues from (at least on full points ties up all lose ends, and the kingdom fully restored). It was adapted into novelized form by Eluki bes shahar as Heir Today, Gone Tomorrow: From the Chronicles of Daventry, Part VI in The King's Quest Companion, 3rd edition.
There are a number of alternate endings for the Long Path but the true ending more or less involves restoring the former king and Queen to life, keeping the genie alive, and reuniting with Alexander's family, and ending the feud on the islands.
There are several less than optimum endings such as the genie's death, not discovering the cause of the feud, not restoring the ferry, etc.
The Long Path goes by a number of different names or descriptions including: 'main-path', "Magic Paint" Path, All Puzzles Path, the good ending.