Here's some more.

OVERALL:
Alternate realities are involved

RANMA:
is missing and presumed dead
becomes engaged to someone besides Akane or Ukyou

RYOGA:
marries Ranma

UKYO:
gets poisoned
gets spelled "Ukkyo"

KASUMI:
works at the Ogenki Clinic

Crossovers:
Godzilla appears
Nuku-Nuku appears
Gally appears
Guyver unit appears