Let's spell it out. If your doomsday scenario is the case, then symphonic film music (or any symphonic music for that matter) is doomed and outdated.

but (a) it ISN'T true, thank heaven, and,

(b) if it WERE true, then there WOULD be cause for concern, and your stance of 'Never mind: it's nothing to do with us' would suggest a fortress mentality of older reactionaries who don't give a hoot if their beloved artform dies with them. In which case this would all be a waste of time.