I guess that we can track the development of the filaments while the
respective galaxy clusters continue to disperse. We should eventually
be able to detect change or no change in their spacial dimensions and
density; while change in length is inevitable. For example, if they
grow in length without losing width, depth, and density, then that
would support that they will develop forever. I am not making any
predictions about how they develop, but tracking their changes will
help us to predict their future regardless if we ever directly direct
dark matter.