A Last Stand as a campaign’s historical event, keep the planned TPK ending or allow survival endings?

I pitched to my players that I could try to run a high fantasy Thermopylae-equivalent mini-campaign for them as part of my main campaign's history. So far, two out of three players agreed to participate (the third being unavailable in general due to work taking up most of their time, they rarely even message the group chat anymore... There's a fourth player but no answer and has also not shown up in recent sessions due to lack of interest/commitment as they've told me so I'm assuming they're no longer playing).

For the unaware, Thermopylae is where King Leonidas and at least 300 Spartans (+ other Greek forces like Thespians, Phocians, Thebans, etc.) had a “Last Stand” against Xerxes and held his entire empire back by a week by fighting at a narrow land pass for three days until a Greek stranger revealed a secret mountain path around them, betraying the Greeks for personal reward/riches (that he didn't get anyway).

Originally, I wanted to run this mini-campaign to test how my players would play their characters inevitably dying in combat but they can leave lasting legacies through other objectives/successes (sabotaging the enemy permanently, hearing how many civilians relocated, sending a message/plan/secret to allied NPCs, stealing something valuable, etc.) and this could influence the present-day of my campaign.

First things first, they agreed that participating in a Pass of Thermopylae-style scenario could potentially be cool, so this isn't a mandatory idea, they could've backed out of it but didn't...

However (and obviously), before I got past my message of "Thermopylae" and "Last Stand" I've been messaged by my players:

1. Player A asked if they can play as that Greek traitor who exposed the secret path or even play as a member of the enemy team.
2. Player B asked if they can reuse their amnesiac character as in a pre-amnesia version so that he can "survive until the main campaign" and is protected by continuity laws.
   1. but this player told me they're also prepping two brand new characters just in case I say no to the first idea.

Them being history enthusiasts, they know what happened in Thermopylae and believe this is a potential TPK. I told them I'm still pondering on how to end the mini-campaign (whether as an alternate-ending or just something to get them used to the possibility of their characters dying) which leads to this.

On the one hand, there's the initial idea of ending in TPK so I can see how they "go out with a bang" and also what could pop up in my present-day main campaign but I've searched in this sub that this is generally a "tricky" pitch and might alter player immersion if I don't give them meaningful objectives/actions (hence the aforementioned lasting legacies), while overall feeling scripted like a book instead of it happening via roll of the dice or with a small hope of rescuing their characters.

On the other hand, letting the players still choose other survival routes beyond killing all enemies still allows for agency and could mean additional future plotlines or even NPCs, and I CAN write arcs surrounding those decisions and survivors... But it also means that players could just choose to avoid death by abandoning their dignity/duty/honor or by being "off-screened" and thus no confirmed body. There's also the additional concern of whether this runs counter of how I proposed they make their first long-term characters in the main campaign.

For context on that last sentence: As our main campaign is their first ever, I told them to make characters that don't start out with heroic/veteran-like backstories as they'll be starting at level 1 and thus are fragile. Player A didn't believe it was that big of a deal and made their character from their old fictional story where she is a rising revolutionary and has a predetermined ending... Before being shot down to unconsciousness and had to roll Death Saving Throws by goblins in their first quest in my campaign. Then Player A told me that apparently this former-character was in the middle of their revolutionary arc and thus has to figure out how to justify being downed so easily. I told them that they shouldn't have done/assumed that as it was against my campaign expectations/precedent and it evidently led to Player A's conundrum that shouldn't have existed. We discussed that the character leave the party if they wanna keep their book-version trajectory (thus becoming an NPC if they ever appear again) while Player A uses a different character with a less predetermined/complete plot.

As the main campaign is currently, everyone's characters are at level 4-nearing-5, so it's possible for the players to have more fleshed out stories and arcs, so I could potentially allow Player B to keep their first idea, but I'm worried this'll turn me into a hypocrite because of what I talked about with Player A in the first session.

So what to do?

• A.) Keep the original TPK-ending, don't allow survival routes, focus instead on legacy-based objectives/encounters?
• B.) Allow survival for both Player A and B, but don't let Player B reuse their main campaign character since they are gonna make new characters anyway?
• C.) Allow survival for both Player A and B, and allow Player B to reuse main campaign character for future campaign subplots/arcs?

And what about Player A? Do I allow them to play as the Greek Traitor if they want to? Do I just simply say (assuming we're going for option B or C) that they can choose their own ending/route in the Thermopylae-like mini-campaign and then let them decide whether to go through with being that Traitor or make a new character?

And what about Player A playing as the enemy team? It is less likely since it adds complications to scheduling and planning as well as there being only two players, but I'm still asking you guys if I should allow them the option to and if there's an opportunity there that I'm not imagining yet and is worth splitting up the only two players for.