An NRI married under the Hindu Marriage Act is still covered by that law, even if they now live abroad. So, Indian courts can handle their divorce case.
Under Section 19 of the HMA, the case can be filed where the marriage took place, where the couple last lived together, or where the other spouse currently lives. In some situations, it can also be filed where the person filing the case lives.
Indian courts can hear an NRI divorce case as long as the marriage was done under Indian law, there is some connection to an Indian place of jurisdiction, and the other spouse is properly notified about the case.