If those songs are then transmitted, sung differently, adapted perhaps, changed over time, then the "process" continues. Difficult, perhaps, in an age where everything is documented, recorded, filmed and set in stone.

More or less impossible, I think. I do Mr Tambourine Man from time to time; it's Dylan's words and tune (mostly) but not his style, not least because I do it without a guitar. But there are never going to be multiple Tambourine Mans (Men?) - except to the extent that the Byrds' version is an established variant - because anyone hearing the song performed can go straight back to the source. The folk process has been killed off by recorded and broadcast music, just like steam locomotives were killed off by diesel. Stuff happens.

If the folk process is finished and the body of songs that we have is complete, unchangeable, and signed, sealed and delivered - then why sing them at all?

Speaking for myself and not for Jim, because they're bloody good songs, and they're good in ways that most contemporary songs aren't. And enough people still* know them to make them fun to sing in company.

*This long after the Revival.