Doctor Who: 8 Theories About Ryan And Graham's Departure In Revolution Of The Daleks
7. Their Departure Is Only Temporary
Speaking of Martha, there's a chance that Ryan and Graham's departure could echo hers in more ways than one.
While Martha did leave at the end of Series 3, she only did so after giving the Doctor a mobile phone, promising him that she would be in touch. Skip forward a year, and Series 4's The Sontaran Stratagem saw Martha keep that promise, calling the Doctor to Earth to deal with an alien attack by the iconic potato men.
So what does this have to do with Ryan and Graham? Well, despite it being confirmed that Revolution Of The Daleks will be their final episode, there's evidence to suggest that Bradley Walsh will have a role to play in Series 13, which is currently filming for an anticipated 2021 airdate. If this is true, then maybe Graham's departure is only temporary, and he'll continue to appear in the show as a guest during Series 13.
A good comparison here is how Russell T Davies used Wilf during the Tenth Doctor's era. Wilf appeared in the 2007 Christmas special and then was an infrequent guest during Series 4, before having one final adventure in The End Of Time. He wasn't a regular companion, but he popped up every now and then, and it was a delight to see him when he did.
Considering that Graham is a fan-favourite - just like Wilf - Chibnall might decide to use him in a similar way. Hell, both characters even feel the same in that they're lovable father figures, the perfect type of personality to bring back for the odd guest slot.