Most people are using a browser with Flash Player built in, and most other people have Flash Player added as a plugin. So Flash is still around. AS3 is also used for making all AIR apps.
It's only mobile web browsing that needs HTML5 instead of Flash, so if it's important to convert your swfs to work in mobile browsers you would need to do the code changes by hand.
Many of the lines could be deleted, like the package details, any import lines, any variable types. You then would convert what was left to work with CreateJS syntax.
What I do with flash is basically create ELearning packages for courses. Now I don't quite use web but I do have a moodle platform that would work better (due to scorm) with html. It still sounds like the only way is to redo your work which is a shame but I will take what you said about placing the referring lines to the symbol its attached to.