Rift: Stretch it into multiple episodes to give something as momentous as the breakup the dignity it deserves. One Xena-lite episode and one Gab-lite episode, each with guest character sidekicks, where each is put into a problem she's not good with, and realizes how much she relies on her other half and loves her despite the trauma. One final episode where they reunite and have a serious talk about what's happened, pledging to stay together and work through the heartache while dealing with Hope.

Callisto does not become a god. I don't know how it would play differently but she's just not needed after she's put in Tartarus.

Athena debuts seasons earlier than the Twilight and complicates Xena that there is an Olympian she feels she might actually be able to trust, especially since she can help put down Ares whenever he causes too much trouble. A slow disintegration of the relationship happens over Season 5 as Athena chooses her family over Xena's friendship, making her death in Motherhood one that Xena actually regrets.

Nemeses for Gab:

While keeping Callisto mortal, Velasca doesn't become a god either. Instead she lives and splits the Greek tribe into factions loyal to her vs Gab. Amazon episodes become political stories that Gab has to navigate to really prove her worth as a Queen. Xena can kill Velasca as Gab's champion, but Gab masterminds persuading the tribes and getting her into a final battle.

Alti: Gab is far more spiritually inclined than Xena. Out of love for her, she learns to become a more powerful shaman than Xena and takes ownership of Alti, who threatens her future with Xena, and Xena's child, as much as she did the Amazons and Evil Xena of the past.

Bellerophon: Gab asks Xena to step aside and let her face Bellerophon alone after helping her get into his fortress. A Hercules-like half-god, he is the toughest opponent Gab has ever faced alone. She defeats him both to avenge the Amazons and to demonstrate the culmination of six years' fighting alongside Xena.