I understand there are "neo-pagan" religions, but from what I've read these are modern interpretations of religions that died out. Have any other polytheistic or pagan religions survived intact?
This isn't my area of general expertise, but for what it's worth
Hinduism, like other Asian faiths such as Buddhism, Taoism, Confucianism, Shintoism, etc. was relatively shielded from the direct effects of Christianity. Christianity rose in the Middle East and generally spread westward instead of to the east. The mythologies of Germanic, Celtic, Roman and Greek peoples, amongst many others, were directly in the line of movement as Christianity spread following the Jewish diasporas in 70 AD and in the early 130's AD.
Christianity did spread eastward, but not nearly in the strength that it did in moving westward through the Roman Empire and around the Mediterranean.
This is not something I'm incredibly familiar with, but as I've heard it explained:
Hinduism is very good at adapting/absorbing religions it encounters. The line "As people approach me, so I receive them. All paths lead to me" is spoken by a manifestation of God in the Bhagavad Gita, a Hindu holy text. Hinduism's ability to absorb a new religion through this concept could make it more resistant to proselytizing efforts.
Again, this isn't my territory, so if someone says I'm off-base then they are probably right.
Are you sure about most other polytheistic religions being wiped out?
Christianity and Islam did a pretty good job on Europe and the Middle East, but there are an awful lot of polytheistic faiths throughout the rest of the world, even excluding European neo-paganism. Aside from Hinduism, Shinto, Vodun and Taoism or traditional Chinese religion, just off the top of my head, there are a lot of traditional or indigenous polytheistic faiths in Africa and South America that I couldn't even name for you.
You're sort of begging the question with the christo/eurocentrism here.