7 Moments That Almost Killed Doctor Who
6. Patrick Troughton's Departure
After the concept of regeneration was introduced to keep the show going, Patrick Troughton played the role for a few years. Doctor Who had found a means of continuing when the actor playing the main character departed, so it seemed possible that it could keep going indefinitely.
Unfortunately, the reality of the situation made that less and less likely as Troughton got closer to leaving the show. One of the main problems the series suffered from under the Troughton era was a decline in ratings. That's usually a death sentence for any program, even one with a replaceable main character.
Another issue that hampered the success of Doctor Who was the transition into color, which came as the series progressed into the 1970s. Losing Troughton and having to replace him when the show was already transitioning into another type of medium threatened to cause a further loss in ratings.
Talk of wrapping things up on the series was floating around the network throughout this period. Fortunately, the series powered through and cast Jon Pertwee to take on the role of the 3rd Doctor. The ratings were still a bit rocky, but the series managed to push through and survive.