He could still sue but :
- Does a US court have jurisdiction on a foreign company operating from a foreign country and that has no legal entity in the US ?
- Even if they could, what can they do other than prevent that company to make any business in the US ?
- And then, can't the OP just make another company in his country that would buy the assets from the previous one ?
no, it's near-impossible to sue unless they have a physical presence in the United States.
Additionally, an American investor can't be an individual investor in an Indian corporation.
If they really wanted to be on the "up-and-up", the American investor would have set up an American company, with the Indian company as a 50% investor. Then, the Indian company would sign a legal document assigning all copyrights to the American company.
Since nothing was on the up-and-up, and nothing was even signed (I hate email/telephone contracts), the American investor has very little leverage. Since he's threatening to sue, I would exploit it.
(I don't know the answers to those questions)