Given our observation of the 'laws' locally the assumption that they hold universally is the simplest explanation. It would require something a lot more complex than what we generally observe for such laws not to hold universally.
The places where the laws break down (big bang, inside black holes (do they) and other extremities) are as far as we're concerned not places we are likely to visit and are nice examples of how forceful you'd have to be to get out of the set of laws that we observe locally. It's probably safe to say that any place where the universally observed laws do not hold are places where energy levels are in play that we'd do best to avoid.
Because the density of the neutron star and the Red Giant are so different (average Red Giant density is about the same density as water), the neutron star can keep a distinct structure/orbit for 1000 years or so. When it gets to the core, fusion occurs in a halo around the neutron star instead of through the normal sort of fusion you'd get in a Red Giant core. This leads to a different ratio of nuclear isotopes, which is how you can determine these objects aren't typical Red Giants.
The resulting objects survive around 70 million years before the neutron star core absorbs enough mass to turn into a black hole. However, the predicted rate of birth/death of these objects indicates there may be a few of these in the galaxy at any given time.
The Interstellar drives cannot get here fast enough! What else is out there?
