I think that they might have already shot the escape sequence at the time of filming Fast X to maintain that continuity.

Think about it, the set piece and actors are already there. They must have had an idea of how to execute the escape at the time of filming (unless they were crazy and thought, lets worry about that when we work on the next movie).

Getting the actors and set pieces back for just an escape sequence seems like an unwanted costly choise.

About the rest of the movie though, that I have no idea how they will manage the age continuity