Well, those are good questions, and ones that have been asked many times. As an American who spent 18 months in Kashmir, the best answer I can give is that your answers will depend on who you ask. Opinions and ideas vary, even among pro-freedom Kashmiris. Which is exactly why the plebiscite that was promised decades ago needs to be held. However, I'll give my answers/opinions, for what they're worth:
1. I see no reason why Kashmiris settled in India or anywhere else would be required to return to Kashmir should Kashmir gain independence. I mean, there were Indians in the US and the UK at the time of Independence from Britain - they didn't have to return to India, though I'm sure some did voluntarily.
2. As I said, I'm in America, and while there is prejudice here, certainly, most people in the United States don't even know where Kashmir is, much less know about the conflict. They look at all "brown" people the same, whether they're from Tamil Nadu or Saudi Arabia. A Sikh gets mistaken for a Muslim all the time. So while the State Dept may have issues, they'd be no more or less than they are now with regard to South Asians from whatever place.
3. Kashmiri Pandits have always been welcome to return, some already have, some never left the Valley. Your esteemed Jagmohan was the one instrumental in their exodus in the first place; that's hardly a secret or conspiracy theory. It's my belief that a good deal of the brutality inflicted upon Pandits was directly or indirectly engineered by his gov't in "false flag" attacks. Oh, I'm sure there was a militant hand here and there, especially going after "informants" - that applied to Kashmiri Muslims who were fingered as informants, terrorized and killed as well as Hindus - but the conflict never was about Muslim vs. Pandit. One of the big misconceptions India and the world has about Kashmir is the notion that it is an exclusively Muslim state. It certainly is a Muslim-majority region, to be sure, but there are MANY Hindus living there. I saw them, I knew them, they ran shops, taught my kids in school, were my neighbors and friends. The same applies to Sikhs. Given the relatively small population of Sikhs per capita in India, I was amazed at how many there are in Kashmir. The school my boys attended was founded by a Sikh and had many Sikh students. There are Christian churches dotting the area as well, and I knew Christians there living peacefully side by side with Muslims; and of course there is the overwhelmingly Buddhist Ladakh. I'm veering off the "right of return" question, but my point is that Kashmir is a veritable melting pot of religious beliefs, which is as it has been for centuries and should be.
4. A true plebiscite should be conducted throughout all of J&K, including any territories administered by China and Pakistan. Whether these countries would agree with a plebiscite being held is up to those countries - I'd like to believe they would, in the interest of resolving the dispute, and there has been talk in favor of such action by these nations. Perhaps that's insincere on their part and naive thinking on my part; but in any event, Ladakh would have to be included with Jammu and Kashmir at the very least, with the majority vote being the final say in the matter. No one said this would be a simple "check India/Check Pakistan/Check Independence" sort of process - I think given the current situation that the process will be extremely difficult. Hence an international observer would have to be involved, in the form of the UN, most likely.
5. The general view is NOT independence for only the Kashmir Valley but for all of J&K and in the interest of a complete free Kashmir, and avoidance of future dispute, all territories recognized as being disputed/occupied by foreign elements ought to be included.
6. The answer to your last question is, I don't know. No one but God knows the answer to that question.