Re: Sanathana Dharma - will this continue its record of longivity?
I am glad you agree that anyone can be an Avatar and no profession or nationalities are excluded.
About what the Avatar will do, actually you are partially right. The new Avatar (the Imam Mahdi (pbuh) as I believe) will sort things out for all of us (Muslims, Hindus, Christians) and correct any misunderstandings that are there in all our beliefs.
I don’t think we should presume to predict what he will teach. But many will be disappointed, especially those with rigid and very fixed beliefs and dogmas.
As I said Hinduism is very flexible, so it will survive even if he says there will be a judgment day (I don’t believe there will be one). Very rigid religions will face a major crisis. A new age will indeed start, we just have to wait and see how it is and have faith that it will be for the best.
With reference to the OP - this is actually somewhat on topic, since it suggests how Hinduism has survived and will continue to do so. As far as Hinduism is concerned, this new age may just produce a new set of scriptures - maybe called the Mahdi Puranas ? (hopefully no one takes offence if I say that)