[Has anyone addressed the possibility of a fracture in the Gnutella network? In any situation where you have only a certain number of connections, you run the possibilitiy of the network fracturing into two or more different networks, independent of each other's existence. Are there safeguards in the system to ensure that this doesn't happen?]

No, there are no safeguards, and the fractionating is already a problem, for it is truly possible to be 'imprisoned' into a small subnet.
Fortunately, since 'ip-servers' are common, this issue was partially mended. In my experience every 20th or 30th log in I get trapped in some kind of small subnets. This is difficult to notice, though - but if your horizon will not rise over, say, 500 and you (using common searches) are getting much less hits than usual it is probable you are 'trapped'.

Greetings...