I wouldn't think so since losing the primary neutral should not affect the delta connection that would be left, and with the 40 amps he is seeing on the grounding, I would not believe this to be primary current since the primary current on the ungrounded conductors would be barely over 6 amps at 19.5kv's,
so this looks more like a possible secondary load that is being used for something else that is directly run from the transformer, maybe a fire pump room with an XO bond on a transformer in it?
street lights? if measurements were in daylight, that should rule out street lights, just don't know,
or why this grounding conductor is the only path for this current, seems strange, thats why I thought of it going to a water pipe and maybe a service connected to the same water pipe, with a lost neutral next door or down the road, but who knows?
but I would still not disconnect it.