For a machine-phase civilization, the only one of these that seems plausible is 3c, but I can't think of any reason why no one in a given civilization would want to leave, and assuming growth of any kind, resource pressure alone will eventually drive expansion. If the need for civilization is so psychologically strong, copies can be shipped and revived only after specialized systems have built enough infrastructure to support them.
It seems far more likely to me, given the emergence of multiple civilizations in a galaxy, that some technical advance inevitably destroys them. Nanomedicine malfunction or singleton seem like the best bets to me just now, which would suggest that the best defenses are spreading out and technical systems' heterogeneity.
A machine-phase civilization might still find (3a) or (3b) an issue depending on whether nanotech pans out. We think it will, but we don't really know, and a lot of technologies turn out to be profoundly less capable than the optimists expect them to be in their infancy. Science fiction authors in the '40s and '50s were predicting that atomic power sources would be strongly miniaturized (amusingly, more so than computing devices); that never happened and it looks like the minimum size for a reasonably safe nuclear reactor really is a large piece of industr...
We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.
Major types of hints are:
Data for:
Data against:
To me it looks like life, animals with nervous systems, Upper Paleolithic-style Homo, language, and behavioral modernity were all extremely unlikely events (notice how far ago they are - vaguely ~3.5bln, ~600mln, ~3mln, ~200k or ~600k, ~50k years ago) - except perhaps language and behavioral modernity might have been linked with each other, if language was relatively late (Homo sapiens only) and behavioral modernity more gradual (and its apparent suddenness is an artifact). Once we have behavioral modernity, modern civilization seems almost inevitable. Your interpretation might vary of course, but at least now you have a lot of data to argue for your position, in convenient format.