1. Even if one of the spouses later becomes a US citizen, the marriage of two Indian nationals that took place and registered in India is often considered as valid. The marriage is still legitimate notwithstanding the wife's change of citizenship.
2. If the husband wants to divorce, he can file for divorce in India where the marriage took place. However, he needs to fulfill the residency requirements. Even though the wife is now a US citizen, it’s still possible to file for divorce in the US. But according to the latest Supreme Court of India ruling, the grounds for divorce should be recognized by Indian law.
3. In terms of alimony, it’s generally the husband who is ordered by the court to pay to the wife for sustenance, while and after undergoing a divorce. The court considers various parameters to decide on the amount to be given as alimony, including: income of the spouse(s), their standard of living and financial status. If the wife is working and drawing a salary that covers her living expenses, the court will certainly take that into consideration along with the husband’s income.