Always the fundamental question of migrant cultures.
One extreme, you have groups from Hungarian Roma to Belizean Mennonites, who never let go, to other extremes, such as the Jews of Alexandria or the Picts, both of whom just disappeared within a few generations of migrating to metropolises, or being subjugated by outside migrants.
Hinduism has an advantage over other religions of migrants to the US, Hinduism can and already has for the most part absorbed (adopted, pick your verb), all of the major Gods and deities of the present American population. If ala carte spirituality is the future of the US, Hinduism will have a place at the buffet.
The Roma traditionally adopt the religion of the nation they live in. For Alexandria's Jewish community, look to Medieval Moslem Spain.
They didn't just disappear ~ that was not allowed. They moved.
Jews always move.