I forgot Invasion of Time had just been released in the UK. If I’d remembered that, I would have tried a different argument. 🙂
The execution of the departure of Leela set the companion departure bar so low it would be impossible to trip over.
That was completely botched. Leela was the companion that really didn’t fit the pattern of the other companions from the very start. She needed something different.
With some of the other “I’ve fallen in love and am leaving” episodes (Susan, Jo) there was a little bit of the plot during the story that built up that possibility. With Leela and Andred, there was nothing. In fact, I rather thought she disliked him.
Having her die to save Gallifrey would have been the best option. Unhappy for the kids, no doubt, but fitting of her warrior ethic.
The Chinese have a saying, “the best stories have sad endings.” While not always true, there is something to it.
Here’s a scenario for the New Series I would have bought… let’s say that, instead of a regeneration at the end of New Series 1, they’d had Rose’s departure. They’d picked up Jack a few episodes earlier. If, over the course of those last few episodes, they’d played out a budding romance, I could possibly see Rose leaving.
Same with her and Mickey in New Series 2. If Micky had stayed in the TARDIS and continued to grow, maybe, just maybe, I could have seen Rose realize the futility of her love with the Doctor and see Mickey anew.
It’s only when the characters have to face their choices that we could see a potential motivator for them to leave.
Would Donna have left if she’d seen the guy from her Library fantasy world? I don’t know… maybe.