If there's one thing that Doctor Who has taught us, it's that time is not stationary. It's not a fixed, permanent thing that will always play out in one specific way.
It's like when you throw a stone in the water, and all those ripples head out in different directions: a single action can cause time to move down multiple different paths, meaning that the fates of certain characters are constantly in flux.
As well as being true in-universe, this is also true when it comes to the actual production of the show. There are many characters in Doctor Who history who came dangerously close to receiving a different fate than the one they ultimately got - maybe they were originally supposed to die, but in the end, they lived! Or perhaps a long-term plan for their character was abruptly cut short.
What's most interesting about these changes is that many of them were made at the last minute (in some cases, the original ending was even written and filmed), meaning that these characters came very close to concluding their Doctor Who arcs in a radically different manner.
10. Margaret Blaine Was Meant To Join The Shadow Proclamation
Margaret Blaine - alternatively known as Blon Fel-Fotch Passameer-Day Slitheen, but quite frankly, that's exhausting to say out loud - was a highly entertaining villain who squared off against the Ninth Doctor in the first series of the 2005 revival.
Best described as a "space criminal", Blaine was ultimately brought to justice by the Doctor, with a little help from the TARDIS. After staring into the heart of the Doctor's machine, she regressed back along her own timeline, sending her back to the very beginning. This turned her into an egg, giving her a fresh start at life in the most literal sense possible.
This is the last time we saw Blaine onscreen, but initially, then-showrunner Russell T Davies had further plans for her character - plans that ultimately never came to be.
In 2008's Series 4 finale, The Stolen Earth, there's a scene where the Tenth Doctor visits the Shadow Proclamation, an intergalactic police force. As it stands, this is a very small scene with a tiny amount of characters, but in the "big budget" version, Davies envisioned an enormous amount of alien creatures packed into the room...
...and one of these characters was going to be Blaine, in Slitheen form.
In fact, this came so close to happening that actress Annette Badland even recorded her dialogue, but when Doctor Who's greatest enemy - budget restrictions - struck, the scene was scaled back.