There's a lot to what you say, about traditional instruments being banned, but in practice, it really wasn't too much of a problem. Settlements were sufficiently isolated that music, song, story could still flurish. And I can really only talk about Ireland, where the Gaelic was forbidden. In Scotland, I think the political climate was much harsher, particularly after the Highland Clearances--which indeed forced many Gaelic speakers overseas. In Ireland, the Blight did damage the oral tradition and music too. But lilting, mouth music or call it what you will is very popular in Celtic societies, whether they're Cornish, Irish Scottish.

Dave Murphy