In Series Eight, there were two main story lines involving the Doctor. First, The Doctor needed to answer the question of whether or not he was a good man. Even though he never seemed to answer that question, the Doctor is easily more at peace with himself during this season or Doctor Who.
Yet, it is that second question that seems to have been forgotten. The Doctor spent a great deal of his time seeking out his home planet of Gallifrey, only to end up disappointed when the coordinates that Missy provided him ended up as an empty pocket of space. That quest was expected to be an ongoing theme, at least until the moment that the Doctor could set foot on his home once more.
That quest has been dropped thus far in Series Nine. Instead, the focus has been almost entirely upon that hybrid warrior that the prophesies foretold. While this is certainly an interesting, and important, story to be exploring, it is interesting as to how quickly the quest to locate Gallifrey has been forgotten.
Perhaps this hunt will be explored again in the future. With the different changes that will be occurring in the Doctor’s life, it may be that he looks to find comfort in his old quest. As Clara will be dying in the next few episodes, the Doctor may well go back to his quest for his home planet as a matter of solace.
Bam Smack Pow
It could also be that this grand quest to locate Gallifrey has been tossed to the wayside with different plots and storylines available. It certainly would not be the first time that an intriguing plot was discarded along the way, and with Steven Moffat in charge, it may not be the last. This move away from what had been a truly interesting plot is a bit puzzling however.
Of course, no one, even the Doctor, could say what would happen should he rediscover Gallifrey. His home planet may no longer be the place he had known, and the Time Lords may have changed after the events of the Time War. Likewise, there is the question of what would happen once it has been discovered that Gallfrey was not destroyed as had been believed. That war could begin once more.
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After everything the Doctor will have gone through on this season of Doctor Who, it may be that he revisits an old quest once again. That search for Gallifrey, even if it proves unsuccessful, may be quite cathartic.