my players and I are currently playing a "pre-game" for a whole campaign I have written. I want the players to be aware of the "how did it get to be this way", so I make them play two games 4000 and 2000 years before the campaign settings.

We have already played the first game, which went quite fine, but I had to somehow iron rough edges because the characters don't fit well into the epoch. Typically, I replaced on the fly "flamethrower training" with "archery", and "advanced computing" with "hieroglyphic writing". I plan to change them back to the proper skills in the main campaign.

I have also made some adjustements to the world politics (based on my desired state), with the following issues: I don't want to kill the characters, which requires a little artifacting (super-being froze them for 2000 years, fitted well in the game), and I don't want the players to feel "trapped" and forced into a "tunnel", even though it's exactly what I do. Currently, I think I achieve this, here is how I have done it: I have created 7 different ways to bring the players into a situation where the super-being is "pushed" unescapably into "freezing" them, as a consequence of their acts. I have enticed them into getting themselves into this situation by using their archetypes. One of the players is a brute that wants to fight and the other has a very physically weak character, so he needs to protect the brute from himself. The players created those characters by themselves.

Whatever their choices, they always fallback to that ending, but garner different experiences and items on the way, all of which impact the next games.

Is there a better way to achieve my main goal (bring them into the frozen situation while activating the next game situation) while not bringing a "tunnel" effect?