[Post on my mind today: Blame it on the bus, from Modern Uberdox]
The transience of Jewish communities is an appropriate hallmark of life outside of Israel; Jews are not meant to remain outside of Israel. A big problem, though - at least in my mind - is the death of halachic community services (synagogue, school, kosher food, eruv, mikvah) while Jews yet remain in those communities.
Halachic services are expensive to maintain. Aside from the the obvious issue of financial cost, a great deal of infrastructure is needed just to keep committed professionals in the community.
A community with 4000 Jews in it will likely have no day school for kids, and no kosher food beyond whatever the supermarket happens to stock as part of its chain's offerings. There might be a chavura of some variety, but that's about it. And so the kids who grow up in that community will be missing what could have been a major influence in their lives, beyond what they randomly pick up in the media or on the internet.
Of course, these communities themselves rarely harbor families who would identify themselves as halachah-observant or even halachah-concerned. But for those of us who believe it's important for Jews to have a mikvah, religious education, lulav and etrog and matzah, and so on, what are our options?
Of course, there is Chabad. Chabad offers such communities professionals and services, funding them first before looking to raise the funds inside or outside the serviced community.
There is also NJOP, which doesn't provide people but does provide free programs and materials to those who would run them.
And there is another model, which I've seen operated by Federations. They hire an itinerant rabbi, generally someone older, who does not have children at home, and assign him a set of communities to which he travels and whom he serves.
The goal is not to run a shul. Rather, it is to have a rabbi who does active research (on-line, and through personal networking; we are past the age of looking up "Cohen" in the phone book) to identify Jews in those communities, and offers them his services. Who travels there perhaps monthly to run programs for youth and adults, and who keeps in touch with people between visits. No budget to run a building, not enough for a school - but perhaps enough to provide a spark which might lead a child, when he grows up and moves out, to look for something Jewish on campus, or in his new community.
What other options have you seen, or do you think might help with this problem? Or is it not a problem at all?