But of course ballet will go on superficially and most people would not even notice what has been lost.
I must respectfully disagree about this. And my reasoning? When I first started watching "vintage" videos (of Ulanova, Fonteyn, Tallchief, etc. etc.) I thought their style of dancing looked very foreign to what I was used to watching onstage. But, now, I'm struck by the similarities. Of course there are differences. There will always be differences. The way Alla Sizova danced Sleeping Beauty is I am sure not the way Mathilde Kschessinska danced Aurora. But really, when I watch old videos, and I watch current stars, I'm struck by the continuity of tradition, and not by what has been "lost." To use one example, I recently saw Diana Vishneva and Vladimir Malakhov in Giselle. I then watched the pdd of Nureyev and Fonteyn in Giselle. And I realized that they were great for the very same reasons. Their sense of line, the tenderness of feeling, the synchronization of two bodies into one. Obviously Vishneva and Malakhov are not Fonteyn/Nureyev, nor should they be. But I don't think "different" means "inferior."
That's just my two cents of course.