Thanks @gazumped it sounds like my notes will be retained, but I won't be able to add any new ones:
Exporting to Multi HTML looks promising I did find the tags are retained in the html code, but it doesn't seem easy to search for them later when looking for a document with a specific tag - perhaps too buried in the htm.
I wonder if there is effective software for Mac to browse a huge archive of saved html pages...?
Pdf export creates a single pdf from multiple notes and no tags from what I can see.