Quakers are still very much a going concern, I was at one of their meetings two weeks ago.
Christian Scientists are in steep decline and have been for decades. I can see them folding in the UK sooner rather than later.
I think JWs are doing a good job of keeping members and even attracting a few new followers, compared with most other churches. The latest summer convention is probably the best they’ve ever held in terms of the quality of the programme. They seem to be doing well.