Tecteun survived (Bi-generation theory)
I haven't seen this theory anyway else but I think it makes some sense:
So Tecteun supposedly is killed by Swarm at the end of "Survivers of the Flux" after her confrontation with The Doctor I believe that before this Tecteun had already Bi-generated and this Bi-generated incarnation is already in "universe 2"
Okay so we still don't quite know how Bi-generation fully works in "the giggle" it seems 15 is in 14's future and has been sent back however in the episode "the devil's chord" 15 says his soul was torn in half which implies an actual split? Only the future theory works for this so I'm gonna go by that for this theory.
Firstly how much does Tecteun know about Bi-generation? We know it's a Time Lord myth but has anyone else experienced it we know it can't happen too often to Time Lords as it wouldn't have been a myth if it did but has Tecteun Bi-generated before during the dark times maybe? So she could know how to trigger one or she hadn't figured it out for a long time but did during flux? I guess it is possible it could have just happened without planning but I feel like she used the Flux and released Swarm to trigger her Bi-generation
We know she released Swarm to damage time by releasing the Mouri she even says this was intended, so I think she figured out with both the damage from the Flux and Swarm letting time run wild she can trigger her own Bi-generation so this most likely happens during episode 3 of Flux "once, upon time" when Swarm gets rid of the Mouri making time go wild so I think while the Doctor was in the time storm Tecteun Bi-generated
Tecteun 1 = "Awsok" Tecteun
Tecteun 2 = Future Tecteun (in universe 2)
So Tecteun 1 triggers her Bi-generation into Tecteun 2, Tecteun 2 already knows the fate of Tecteun 1 at the hands of Swarm, Tecteun 2 explains as much as they can to Tecteun 1 (just like 15 did to 14) maybe getting Tecteun 1 to have the conversation with the Doctor at the end of the "once, upon time" episode and bringing her to Division HQ in "Survivors of the Flux" or Tecteun 1 could just do this without information from Tecteun 2, Tecteun 2 goes into universe 2 while Tecteun 1 talks to The Doctor at the end of "once, upon time" about how this universe is over and she released Swarm etc
Then the events of "Survivors of the Flux" happen with the Doctor and Tecteun 1 having their confrontation and then Swarm touches Tecteun and she disappears now this is a big theory of what most people think will happen to 14 is that when he is on the verge of death he will fade and appear back at UNIT as 15 so this is what I believe happens to Tecteun
Tecteun 1 disappears and goes back to the point of the Bi-generation becomes Tecteun 2 and leaves for universe 2.