Doesn't that also mean that (in such a hypothetical situation) our best theory says that our previously best theories will give accurate predictions up until the point at which we observe something equivalent to a galactic-scale collider? If so, that doesn't sound so bad to me.

On the bright side, if there was a single particle that didn't move like a string, string theory would be falsified. On the dim side, it's difficult for anything to not move like a string, because string theory is so powerful as a framework that you can get it to make just about anything consistent. What you really want in physics is a brittle framework that only allows you to slot in a few different behaviors.

It's kind of funny because programmers want the opposite thing that physicists do. When your client asks for a behavior that you have painted yourself into a corner against ever implementing your software has been "falsified," an expensive disaster that you work very hard in advance to prevent! If you made universes for a living, strings would be an ideal framework.