Doctor Who: What Happened To Every Companion?
11. Patrick Troughton Era
The first Doctor had other companions, but they didn't leave the show until the 2nd era, so we're talking about them here.
The first three companions that traveled with the 2nd Doctor were Royal Navy Officer Ben Jackson, secretary Polly Wright, and badass highland warrior Jamie McCrimmon. Ben and Polly were the first ones to leave. Though they were both loyal to The Doctor, Ben was also loyal to the Royal Navy, and thus never lost sight of his desire to return home. So, The Doctor took them back to the same day they left with him originally, and they parted as friends.
Next up was Victoria Waterfield, the youngest companion so far, at only 14-15 years old. Her departure came when the orphan grew tired of the danger, and just wanted to settle down with a loving family. So, despite the pleading of the lovestruck Jamie, she chose to stay behind with a married couple named Frank and Maggie Harris.
Finally there was Zoe Heriot, a brainy girl from the far future. But her and Jamie don't have as fond a farewell with The Doctor. After a nasty adventure against the fearsome War Lords, wherein The Doctor had to break the laws of time to ensure everyone got out alive, The Time Lords - while all too happy to oblige The Doctor's request to punish the War Lords and undo their damage - still needed to punish The Doctor for his crimes.
Both Zoe and Jamie were beamed back to the points where they initially left, only allowed to remember their original adventure with The Doctor, but nothing else.