Doctor Who: 8 Theories About Ryan And Graham's Departure In Revolution Of The Daleks
4. Grace Comes Back To Life And They All Settle Down
It's time to wade into some truly far-fetched territory. On the off-chance that Ryan and Graham's exit does end up being that aforementioned Martha-style "leaving of their own free will" scenario, then the resurrection of Grace is the perfect reason for them to decide to part ways with the Doctor.
There isn't really any cold-hard evidence to support this theory, but it does feel like a fitting final step for Ryan and Graham. Their Doctor Who story has been driven by the death of Grace since day one, so it would actually feel quite natural if the end of their story brought things full circle and allowed them to finally let go of their grief.
It's also worth mentioning that Grace has appeared in the show numerous times since her death (as a hallucination/vision), which could be interpreted as Chibnall trying to keep her fresh in our minds as he builds towards Revolution Of The Daleks.
Maybe Grace's regular re-appearances were Chibnall's way of cementing her as an integral part of Ryan and Graham's story, and so - going back to his five-year plan - what if he's had her entire arc mapped out from the very beginning, from her death in The Woman Who Fell To Earth, to her resurrection in Revolution Of The Daleks?
As for how Grace could be resurrected... well, this is Doctor Who. Characters returning to life really isn't a problem for this show.