Episodes would have to be changed or cut to accommodate some resource or another not being available due to a strike. But there was the time that a union strike against the BBC took out any entire story. The year was 1979 and the story was Shada, a 6 episode serial written by Douglas Adams (Hitchhiker’s Guide to the Galaxy).
A lot of Shada was shot but the strike prevented completion of the episode. The Doctor Who production office held out hope the story could be finished but finally, the call was made to shut down Shada. A day after production was closed, the strike was settled. The producers tried to ramp up production to complete Shada but it was too little, too late.
Another version was edited together using existing footage and bridging narration.
Quick note on the Doctor Who spin off Class. If you thought, "Hey, no new Doctor Who series for 2016 but at least Class is coming this fall, right?", you may need to revisit that concept depending on where you live.
The debut of Class will take place in October 2016... for viewers in the United Kingdom. Over here in the United States, Class will not debut on our screens until the spring of 2017. Which is a very frustrating development. Yes, there were times in the past that American access to new Doctor Who stuff was delayed by months or even years. But we've gotten use to a bit more synchronous cooperation on both sides of the pond in recent years.
But we do have confirmation that the Doctor himself, courtesy of Peter Capaldi, will appear in the first episode. So there's that.
But if you're desperate (and I do mean DESPERATE) for a new Doctor Who adventure, next week, in this space....