Are most immigrant-origin ethnic enclaves only sustained by new immigration?

[Capsicum]

Rural ethnic enclaves settled by immigrants early on can last a while (eg. Amish, Mennonite communities), but it seems like urban ethnic enclaves can only last so long once the immigration that sustains them ends.

Little Italy neighborhoods don't last very long after Italian immigration was no longer a big deal. A lot of former Jewish neighborhoods are revitalized by newer, recent immigrants from Israel or the former Soviet Union, as the older waves assimilate and leave. Even Chinatowns are sometimes starting to go away by Chinese immigrants heading towards the suburbs.

Many ethnic enclaves not sustained by recent immigrants willing to pay a premium to live there often disappear through gentrification (if they are near desirable parts of the city) or go away from assimilation after their kids choose to move away or their specialized shops/products no longer find a demand among their assimilated descendants (unless they can go upscale and be "touristy").

Do most ethnic enclaves really require international immigration to sustain them (eg. another wave of "the same" or similar ethnic groups, such as say other Asian immigrants choosing to live in older Chinatowns), or are there any major cases of native/local born people sustaining an enclave?

What kinds of ethnic enclaves have high %'s of native born living within them, and high %s of that ethnocultural group, or at least a strong local ethnic economy (eg. products, shops etc.)?

(I guess, if you count long-standing African American neighborhoods in the Northern US after the Great Migration, though that's not really an immigrant example, and many of them are products of segregation historically rather than voluntary affinity)

Also, are there ever inter-state or inter-regional migrations that sustain ethnic enclaves? Like for instance Asian Americans (instead of international immigration of Asians) from other states or small towns within the same state moving to Asian ethnic enclaves in the nearest big city? The only thing is that if assimilated kids of immigrants are mobile enough to be willing to move around from city to city, by then, they'd probably not choose an enclave.