Hmm… that’s an interesting and complicated question (this kinda got long and sometimes out of topic, sorry in advance Anon).

Well, to be honest I hope there is hope but redemption is not exactly what I’m thinking about for Seidou.

As I said in a different post before: Seidou’s worst enemy is his own self, he’s eaten from the inside by an inferiority complex that he very probably developed as a child. It was expressing itself through anger, Akira, Juuzou and even with Haise recently in the auction arc, and that is the thing he needs to take care of, if we ever want to see him back on the “good side”. 

The problem is, it’s easier said than done, unfortunately.

Actually, I don’t think saying Seidou is gone is the most accurate, because he has his full memory and brain capacities (he remembered that girl who spoke during the classes, he remembers Akira and his past as a student…), and even though his physical appearance strongly suggests that Aogiri tortured him a lot, I think he is totally conscious of what he’s doing and of the path he’s taking. 

No, the real problem for Seidou right now is that his mind is entirely twisted by what Aogiri put him through but not only, because Aogiri also probably pushed Seidou’s inferiority complex on another level (unconsciously or on purpose, I can’t decide) and as he is now, between the probable torture sessions but also from how he sees himself, he is not exactly gone but rather totally engulfed in this wrong vision he has of the world and of himself.

For example, he doesn’t see himself as a ghoul…

But he’s not a human either, since humans are the sweets and he’s the one eating them.

So how does Seidou sees himself?

It took me a while to figure it out but as a half ghoul, Seidou is stronger than the humans he eats (for example, he killed and ate Special Class Ato and many others) and also stronger than most ghouls (he could take Hina and almost went on par with Sasaki), especially after what Aogiri put him through but also because he’s seen as one of Kanou’s real success (hence his rivalry with Sasaki, who is seen as the best success).  

So yes, I think Takizawa sees himself as death (’once you’re death, death is no longer scary’) and that’s why he preys on those weaker than him. 

It’s all about the inferiority complex: good and bad, humans or ghouls, none of this matters. Seidou is stronger, Seidou became death under Aogiri’s (or rather Tatara/Eto/Kanou’s) hands and if he had the choice, I am not sure he would ever go back to his previous life as a CCG investigator.

Torture is supposed to break men (look at what happened to Kaneki), but it didn’t exactly work like that with Seidou: by being called a successful experiment (unlike Amon for example), the inferiority complex inside his mind pushed him to accept his fate as a half ghoul (even if that meant siding with “that bastard Eto”) because in this life he was no longer a loser, he was no longer scared.

Of course, Eto seems to control him, and there is no way she would let him leave Aogiri (seeing as he is a successful experiment), but I don’t think Seidou would want to leave Aogiri in the first place, not when he’s seen as a success (when he used to see himself as shit before) and when the organization’s name inspires fear to both ghouls and the CCG. 

Don’t make me say what I didn’t say though! I think Seidou is suffering a lot because of Aogiri and yet he still thinks that this life is better than the previous one, because at least in this life, he’s not a loser.
Were he to realize that his way of thinking and of seeing himself are totally off, he would also definitely realize that his life as a half ghoul at Aogiri’s mercy is seriously horrible.

As I said though, it’s easier said than done and I don’t think he’ll manage to recover from all this on his own.

And that’s when Akira steps in. 

This might be an unpopular opinion, but I think if there is one person who will be able to get Seidou out of this unbreakable cycle, it’s her.
Because of that one scene that changed everything about half-ghoul!Seidou’s character:

 This might not be so understandable at first but here is what I think happened:

1. Akira arrives to save Haise and sees him first 
2. She calls his name
3. Takizawa lifts his head, ready to play the “Togi prank” on the one who’s recognizing him (because he’s “death” and no longer loser!Takizawa and he can prove it)
4. But then he sees her, hides his face in shame and flees

And why is this scene important? Because it’s the only time so far in :Re when we see Takizawa hesitating and eventually giving up. He didn’t hesitate when he murdered Ato or Togi, or when he fought Sasaki and Hinami (who technically was on the same side as him) but he fleed in front of Akira. After showing signs of extreme unease to think she saw him “like that”.

So I think it definitely means that Ishida intends to write more about these two since she’s the only one who got such reaction out of him, and knowing the huge crush he very probably (almost undoubtedly) had on her since their Academy days, I wouldn’t be surprised if Ishida was heading towards Akira being the one saving Seidou.

There is obviously a reason about why Akira is the one mentoring Sasaki and, even though ghouls killed her parents, it is shown she cares and trusts him a lot and all I’m saying is that Ishida could use the bond she created with Haise in order to make her the only possible way for Takizawa (and maybe Amon) to get his chance out of Hell. 

Even before the Auction arc, I don’t think Akira ever gave up on these twp being alive (extra of vol 14) and she probably already imagined the worst scenarios, but her partnership with Haise shaped her in a way that she wouldn’t be “disgusted” or uncomprehending about Takizawa and Amon’s situations. She hates ghouls yes, but I think she sees Haise as a human, victim of a mad experiment which turned him into a half ghoul, and it’s also exactly what happened to Seidou and Amon.

So there you go: yes I think Seidou has his chance (not at redemption but at getting out of Hell) and that chance is Akira, because of his past (?) feelings for her and because she knows him.
Out of all the CCG characters introduced in TG, Akira and Seidou have known each other since stepping in the Academy for the first time and I’m sure that for this reason, she has a way to prove to him he’s not worthless or useless.
From the moment Seidou will stop thinking the him of before was shit, he will probably accept to more or less change back. 

And it’s not impossible: she’s the perfect 100-mark, he’s the loser, he had feelings for her but always saw her “from the side”, and the fact she saw him “like that” in the auction arc made him shameful… 

So how do you think he will possibly react when he is to know that the “perfect 100-mark” she is believed in him for 3 years and tried to help him (in the theory that she will be the one to save him)? He will be in deny at first, but it could still save him from everything… 

–

As for your second question, I don’t think Akira will ever make the choice to save one more than the other; if she can, I think she’ll save the two of them, even if we don’t know yet how Amon is holding up mentally and if he actually needs help. 

Amon escaped from Aogiri and is on a constant fight with them while Eto wants his head, but unlike Seidou he’s somehow free and I’m thinking he is sane, when I see how he can track Aogiri ghouls and fight them while leaving the “good side” (Saiko for example) alone. So Amon might not need “saving” in the same way as Takizawa (who preys on both ghouls and humans, good and bad not existing since he’s “death” and stronger).

However I don’t think Akira will ever choose between the two of them, because as she said:

Yet if one needs her more than the other, then it would make sense that she ends up helping the former more, wouldn’t you say? 

Err…. This got super long and became an essay of how I see Takizawa Seidou right now, but I hope it still answers your questions.
Sorry for rambling.