Dm scenario question

[Desteplo]

So I have this mind flayer campaign, I modified sea hags to fit as the “face huggers” of the campaign.
They fought two in this house and nearly lost one of the PCs.
Later six chased them down but lost them and they ran into the fighters guild.
Grabbed a 5th lvl fighter, 3rd Barbarian and 8 thugs
They made their way into the sewers and took some tunnels trying to get to the mind flayer and take it down
They got to an intersection. They had 3 choices or go back top side.
Well... mind flayers aren’t stupid. There was an ambush and they quickly made their way to the center.
They led the way and the thugs took the rear
So they had 12 sea hags behind them and 4 in primary combat. The difference being that they had a 5th lvl fighter and a 3rd lvl barbarian on top of their party while the thugs held the 12 others back
But they were flanked. They didn’t target down any specific one down. so 3-4 turns later there are only 3 thugs left alive and 3/4 sea hags they were fighting are at 50%
They had decided to continue the slog until the four they were fighting were dead. Regardless of having another fresh batch of sea hags behind them
I had the lvl5 fighter tell them they need to push past these 4 sea hags and set up a wall to take them out, or push and flee

Here’s my question: should I have just taken the TPK? Their lack of coordination and planning

Or was that fair: they actually did try to coordinate after that

Side note: when I was a player with these people, no matter who I played (introverted wizard that was scared of everything) I was always the guy that decided the plan.
So I know my players. But should I have let them learn the hard way?

[Honest Tiefling]

Talk to them. What matters at the end of the day is that they had fun. If you are worried, I'd let them present their case for why it shouldn't have happened. Personally, I think what you did was fair, if your group does very lethal combats.

Perhaps as an alternative to the TPK, they wake up in a basement filled with things in jars, glass vials and implements of surgery. Their gear and loot is missing, and they don't know where they are. Problem is, they're actually walking experiments of the mind flayers, and need to find help or bad things happen.

[Ivor_The_Mad]

Well normally in our group if a TPK is about to happen we tend to throw in a Fizbop encounter. Though i would say it your choice. If you think that the did poorly then it fine. If you want it to last longer intervene.

[SilverStud]

I don't recommend ever punishing your players. In fact, I don't recommend doing anything to your players.
I don't recommend punishing the characters.

What I do recommend is setting up a scenario and letting it play out. Before you let them walk into an encounter, you should know what your intentions for the outcome should be. It sounded like you wanted them to have a very tough fight, but one that was surviveable. You messed up (small mistake: overestimating their tactical skill :P ) and had to cover with an NPC that told them the solution.

I think you did the right thing! I just don't like the mindset of punishing/teaching/letting-them-learn-the-hard-way DMing.

One thing I do when making encounters is I build myself "outs." Things like "this bandit lieutenant has an inflated ego, and thus sometimes gives his opponents help" or "Door B can be closed randomly (improvise cause later) to disadvantage enemies." And, in the other way, stuff like "these 3 bandits break and run for reinforcements if too many allies die too quickly" or "in three rounds the rear guard catches up with the fight and joins."

If you want your characters to accept your "outs" as logical/world-consistant, make sure you telegraph them. The high-ego lieutenant should say things like "This is a slaughter. It makes me look like a bully!" before he pulls back some troops. I think you get the idea.