Yes, and this is kind of the whole point of the protocol. It just hinges on defining the real stellar network. An analogous question is, "Is there a way for a computer to realize it has been partitioned from the real Internet?" Well, sure. Pick 50 web sites you think are really important--maybe a bunch from Alexa, plus your bank, employer, etc.--and make sure you can reach the vast majority of them (using https, of course, so no one can impersonate them).

There's one sense in which FBA is stronger than the Internet analogy, however, it that is is actually testing transitive reachability. So instead of just making sure you can talk to those 50 web sites, you actually make sure all of those 50 web sites can talk to all the sites they consider important, and so on, until you get the transitive closure, which is basically the notion of an FBA quorum.