Plus companions were coming and going a lot in those days and they weren't considered very important as can be seen by the pretty feeble exits they were getting.
Speaking of 1960s companion exits, whatever happened to Vicki, Sara Kingdom, Ben, Polly, & Victoria?
Of course, the departures of Susan, Ian, Barbara, Dodo(
), Jamie, & Zoe all still exist. Katarina's death is just about the only portion of that episode that still exists. Steven's departure in "The Savages" no longer exists but Peter Purves talks about it a little bit in the Season 3 overview documentary included as a bonus feature on the DVD of "The Gunfighters."
There's also the possibility of contacting aliens and discovering that they've been monitoring Earth from hidden satellites for decades and have recorded all our broadcasts...
While they may have recorded many of our broadcasts, I'll bet they would have wiped most of Doctor Who
because aliens would find it racist.
I'm still holding onto the hope that for a 50th Anniversary Gift, the Doctor will leave behind a case containing all the missing episodes, which he has collected up prior to destruction for us over the years (This may even be why some of them went missing in the first place, because he grabbed the copies to rpesent us for the 50th)
I've wondered about this myself. I mean, didn't the last known copies of "The Traitors" & "The Tenth Planet, Part 4" mysteriously go missing from the Blue Peter
offices shortly after clips of them were edited into a Blue Peter
episode commemorating Doctor Who
's 10th season?
I also think this could be a funny episode of the new series: The Doctor arrives on an alien planet that he previously visited, only to find that they've now turned his adventures into a cheesy TV series. But because of some nefarious alien subliminal messages hidden in the episodes, the Doctor has to steal or erase much of the series.
Come to think of it, the new series has occasionally made nods to this concept. One of Shakespeare's plays was destroyed because witches hid a magic spell in the final speech in "The Shakespeare Code." And Vincent Van Gogh painted over one of own paintings so that he could draw the Doctor a quick sketch of the invisible alien that they were fighting in "Vincent & the Doctor."