In the UK JW numbers have fluctuated around 120,000 to 140,000 for the past 30 years. They are neither growing nor declining to any great extent. But this is in contrast with the vast majority of other churches that are in steep decline. The Church of England, Church of Scotland, and the Methodist church have all declined by well over 50% in that same period.
I thought JWs would decline after the generation teaching was dropped in 1995, and after the Internet became mainstream and ubiquitous around 2000, but it never happened. But I don’t think JWs can defy gravity forever: the same trend of secularisation that affects all other churches will eventually come to them also. That’s barring major word events such as world war, deadly plague, technological upheaval, or the like, which could disrupt long term secularisation trends unpredictably.