to your first question, the same that happens when a democracy turns into a dictatorship. Only since they are borderless it might be easier to leave the sinking ship.
The second question is already a problem now when disputes between countries with different laws are settled. Community A would have to negotiate with community B. What is most important is that community A has promised security against rape and will need to compensate Mary.
Since your example is a quite extreme one it is easy to answer. Either community B makes Tim accept the verdict under community A's law and make it clear that B people are only allowed to rape other B people. Or B would get massive problems with all other communities and would be excluded from intercommunity cooperation. The other communities will apply economic pressure and no longer value other deals with B people. To avoid compensation payments higher security measures would be installed targeting B people.
In essence B people will be separated from economy have to fear for their safety and eventually have to move to a little island where they can all rape each other in peace.
In addition it is hard to imagine that you will even find a lot of people joining such a community. People are crazy, but not that crazy.
The hard parts are the little differences like neighbours complaining about too loud music...