Of course they're talking about a geological timespan -80 Million Years. That doesn't change the potential rise over the next 10-100 years. A mere flash in geological time. There is a curious reason, The oceans are becoming deeper. Changes caused by continental drift being the primary cause. For example The Atlantic will widen, and the Pacific will shrink. While they say the estimated drop is around 120 m, if the Ice on Greenland and Antarctica happened to melt, as it seems to be doing today, the drop would only be 70 m

Does anyone really believe this rock will be here in 80 million years?

Our descendants, if there are any will be another species entirely. Perhaps not so suicidal. I've no right to imagine I can guess. Nature as it has been shown, is the mother of invention. The father of invention always seems to be watching nature clean up.