This destruction will lead the anti-matter from the Flux to be cancelled. The Doctor doesn't prevent this from happening but plans to throw the Sontarans into the mix too and effectively wipe them out. A different Doctor who is/was all about saving species no matter whether good or bad. As seen in Journey's End. When the Flux isn't completely destroyed it's Diane (Nadia Albina) who comes up with the solution using the Passenger. As she also comes up with a way for Vinder (Jacob Anderson) and her to leave the planet and get back to be picked up the doctor in the TARDIS. As she was trapped inside the Passenger she has worked out how it works and tells her to make the anti-matter enter the Passenger in deep space and it will become harmless due to the space inside the Passenger.
Finally Vinder and Bel (Thaddea Graham) are united and the Doctor sends them on their way with Karvanista on his ship. He probably needs the company too. It's also Dan (John Bishop) who releases Karvinista from his cage adding he fetched his dog. Diane keeps her distance from Dan who tells her he wasn't late but he was kind of detoured via Karvinista. The Doctor gets Claire (Annabel Scholey) and the Professor (Kevin McNally) to infiltrate a Sontaran base ship and be used as bait so they can get information on the Flux date from using their brains. When push comes to shove and they do get their information, the rings the Doctor has given them only work to rescue Claire as the Professor's one is destroyed as he takes it upon himself to take out some Sontarans, which wasn't really necessary at all. Sadly there was no one ring to save them all. He heads into the Flux too and rather accepts his twist of bad luck and fate. A shame as he could've been used more in future eps. He's more sad he hasn't been able to write an autobiography.
The Grand Serpent apparently underused in this ep as he doesn't even remember Vinder and doesn't carry out much torture on the Doctor. Vinder gets his revenge by leaving him on a tiny space rock, his "exile" just as Vinder spent his 'exile' in that observation station. He didn't even get to get any sort of dialogue with Kate (Jemma Redgrave) as he was hunting her down. Swarm (Sam Spruell) and Azure (Rochenda Sandell) were also underused as creepy villains going back all the way to Hallowe'en they didn't get much to do here. Not even able to exact revenge on their 'master' Time being released. So he turns them to dust before turning into the Doctor and telling her she won't be finished off. So obviously that should add something to the New Year Specials. Especially as the Doctor mentions the Master too. She gets the pocketwatch and tells the TARDIS to hide it somewhere deep down she can't find it unless she wants it of course. Was she afraid to access her past memories and what she was or did in the past as Division operative. Maybe this would've added some backstory into why she's so hellbent on saving, though destroying has also entered the equation on occasion (of course it was just written that way.)
Nothing said about the Flux or whether those civilizations being destroyed with few survivors will have much of an impact on the future and the planets/places the Doctor will be able to 'visit' in the TARDIS taking Yaz (Mandip Gill) and the companions with her. She also returns for Dan to take him with them. The Doctor also persuaded Williamson to return to his own time through the correct door of his tunnels as he had greater things to do and history needed him.
Sontarans gorging themselves on chocolate was a fun scene to move from all this jumping around and throwing so much at the viewer. All 'n' all we got an ending whether it's what we wanted or expected is another thing. Many loose ends were left and you can't help wonder if it was on purpose or if any of it will be revisited and concluded. Kate was left on Earth along with Claire who might join forces. Is UNIT still around?