It’s definitely in decline, it will always remain a regional ethno racial belief system similar to Nordic paganism, Daoism and Zoroastrianism - a large part of that is because it doesn’t exactly have the same appeal as abrahamic religions which are a lot more simpler and most of the world is familiar with all 3 Abrahamic faiths. Just look at the Indian diaspora in any country where it’s been for over 50+ years and you’ll see Hinduism declining - from South Africa to Guyana to Fiji to Trinidad even a lot of western countries, by the second generation most Indians are atheists or Christian, eventually by the 4th generation over 90% of Indians become Christian.
I even see this phenomenon in newer Indian diasporas such as the one in the US, a lot of American raised Indians are non religious or convert to Christianity by the time they’re in college and their children most definitely do not even learn anything about Hinduism, they either join a church or remain agnostic, you can thank India’s state encouraged mass emigration program for that - more and more Indians will immigrate to the west and their children and future descendants (who will be part Indian at best) will not stay Hindu, in about 50-100 years you’ll see a bunch of westerners with Brahmin last names either preaching the gospel or promoting atheism. There will always be some hippy liberals that might coopt Hinduism but it will always be a niche hobby/lifestyle rather than a widespread movement. Occasionally you’ll get some 1/8th Indian kid who will dabble in Hindu mythology the way white people geek out over Greek mythology but it’s never gonna be anything more than a hobby. That said, as long as India remains the cradle of Hindutva then Hinduism will always be alive, it just won’t ever be a global religion and this is some thing its adherents should accept and be okay with and since a lot of Hindus acknowledge that it isn’t a missionary religion and they don’t seek out converts then they should be content with the range of Hinduism, if anything it’s probably better off remaining a regional belief/ethnoreligion like Hasidism and Druze. Any over ambitious aspirations will lead you to disappointment.