In any emergency, abandoning a train to take your chances running across an open field is almost always the wrong thing to do. Especially when you are not aware how many attackers there are and what kind of weaponry they might use.

There will be screams, there will be gunfire, a big problem is the average European citizen will not be able to recognize gunfire, it's not sounding like in the movies, you will see people run away or die in front of you but you need to stay calm and be aware of your surroundings.

The first thing you need to do is get emergency services on the line if you have any kind of connectivity. Do not assume someone did this before you. Maybe the attack just started a compartment ahead of you, maybe everyone who could call emergency services is already dead. So the sooner you get help, the sooner this will be over.

What you need to realize is that you are not able to run away and make it, because in a Train you are basically trapped and if an attack happens you won't have any information that helps you make the proper decision where it's safe and where a kill zone is.

In a Thalys you will most likely be sitting in one of the open compartments like this.

https://upload.wikimedia.org/wikipedia/commons/b/b3/Thalys_Comfort_1_car_overview.jpg

https://upload.wikimedia.org/wikipedia/commons/e/e2/Thalys_Comfort_2.jpg

So first of all you need to identify from where a possible attack might come, people rushing at you from one side of the train in panic / injured might give you reliable information, maybe you find time to ask someone.

In any case you need to get into a strategical position where no matter the final outcome you significantly better the chances for your own survival and those of the other passengers. Keep telling the emergency services what you are doing / hearing and give them any kind of information that might help them, it's always good to keep the wagon number from your ticket in mind for any kind of emergencies, derailing, fire, etc where you might need quick help.

Looking at the above pictures you will see that in those open compartments there is a wall besides the glass door and enough space to stand on a seat or directly besides the door. That is where you want to be, so make your way through the people running past you in panic, no matter if you have to kick, punch, throw, scream at or scratch them to get there, you want to be in that spot before an attacker gets through that door.

You will need both of your hands free so put the emergency services on speaker and just put the phone down. Your job now is to take a deep breath and concentrate on that door.

If someone comes through that door with a weapon or actively shooting at the people in your compartment you want to bring him to the ground with everything you got.

You don't want to put handcuffs on the guy to arrest him or killing him. You want to stop him from shooting, bringing him to the floor and containing him on the floor so he can't continue his violent action.

There will be people helping you once you brought him down. But even if they are not you are doing the best you can do give yourself and the people you care for / around you a better chance of survival. Even if you don't make it you earned yourself a pretty decent "Get out of Hell free" card.

Now all of this sounds really awesome and plausible, but the ugly truth is that you are most likely going to die.

If you are in the wrong place at the wrong time you can be the most badass special forces operative on the planet, you're simply f*cked.

No matter how well you are prepared or think you are prepared you might react completely different in that situation if it actually happens.

You might tackle the guy and bring him to the ground, and then get shot in the head by another guy cleaning up behind him.

Or attackers might come from both sides of the train, or use gas or chemical weapons. Flashbangs or fifty other ways to make your last resort plan go down the river.

But as you can see your survival chances staying where you are are significantly better than running away or even trying to get outside the train.