You mention FSP in the title but then leave it out of the analysis, and I think it passes your test. Most are staying there, most don't have the resources to just up and move out, there is a strong community (and many strong sub-communities), and they do support each other. It's comprised of several thousand (not including sympathetic locals/natives, of whom many several thousand more), many are families and many (I would guess substantial minority) are religious, and it's been going for 18 years now and accelerating. If the FSP community were targeted for persecution by local, state, or federal, I think there would be significant community mutual aid.
This relates to my general thinking about community. A strong community seems to be one where the people are willing to die to protect it. Obviously, the stronger the community, the greater the willingness to die. The weaker the community, the less likely people are willing to die to protect.
I think one of the metrics I have for the viability of a community in the long term is this question:
Are the inhabitants willing to die to protect this community?
If not, then when economic opportunities change, the people will simply move away. When the threat of death becomes strong enough, the rich people will make an excuse to move away. In the case of Liberland & Sea Steading, they are all rich enough to move there, and rich enough to move away with a snap of the finger.
Commitment. Skin in the Game.
If you have a bunch of godless, childless libertarians move to one area for better tax treatment, you may discover they have zero interest in sacrificing their life to protect it. They'll just scurry to some other tax-sheltered country.
That's how I view the community in Puerto Rico for the low tax incentives. They all have businesses that they can pretty much manage anywhere in the world. There cannot really be any worthwhile community, because at the end of the day, once the tax incentives are gone, so are the people.
When a hurricane is about to come, everyone will fly out.
When the power goes out all over the island, everyone will fly out.
When the IRS goes after one of the members in the community, no one is coming to the rescue of the person getting audited.
Every man for themselves because they are rich enough to not have to rely on others.
Not much of a community at all.