Let's assume we have one rod that meets the 25ohms requirement, and no other paths other than earth.
I'm interested in three things:
1. Can a dangerous potential exist at the rod with an otherwise compliant configurations (other than than the lost neutral).
Not really. I believe one would have to posit multiple problems to have a serious danger. E.G. hot-to-ground fault
plus lack of effective ground fault current path. Or open neutral
plus lack of proper grounding electrode. I believe that generally speaking, having the rod, and being closer to it, makes things safer than not having it or being farther away. I can't think of how a properly connected electrode makes a situation worse. An open neutral without a grounding electrode (or perhaps worse with a
disconnected grounding electrode) strikes me as a much more dangerous situation than an open neutral on a properly grounded and bonded service.
Of course, one cannot assume that there are no other problems. If you are being called to the site because there is one known problem, the chances are not zero that there's another, unknown problem. I'm sure someone has developed a protocol for being careful when approach an unknown situation, but I'll see what others suggest in terms of specifics. Common sense tells me: wear insulating gloves and test for voltage.