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If it's traditional TN-C with no nearby CNE
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Oops, typo here, this should of course read TN-S
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gets interesting if a TT neutral to the building becomes accidentally disconnected
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I think you've done it as well, I guess you meant to say TN-C-S neutral. Working with true TN-C (CNE from origin to load) is an eye-opener when the CNE isn't a high-integrity conductor like earthed-concentric. I first did this in Germany in the 1980s - it's called 'klassische Nullung' - where the old grey PEN conductor in a lighting circuit had to become both neutral and earth at a metal fluorescent batten. Disconcerting until one's initial jiitters about the thing going open-circuit calm down.
My comment about the retrospective TN-C-S for the solar inverter being potentially dangerous (see what I did there?) ws referring to two different 'versions' of earth, one from the rod and one from the neutral, existing side by side in what is supposed to be an equipotential zone. The TT earth becomes an unbonded extraneous conductor relative to the TN earth.