Post development, the characters that had not returned was the following:

Zimilon (Missing since 2004)

David Lega (Died in the original story, did not return subseqently)

The Twin-Swords Sibling (Missing since 2005)

Grant Lega (Pre-timeskiped character that did not return from the old timeline)

Omega Final (Missing since the timeskip and not in the subsequent versions)

Old-Crenval (Missing since 2005)

The Dark Elementals (Missing since timeskip since 2005)

Talvix (Missing since 2018)

Zelazon (Died 2019)