Why would we assume Offenhouse managed his own portfolio, or more exactly, failed to arrange for its management after his death? He specifically says he needs to contact a bank on the issue, and also that he needs to contact a lawyer.
I just can't see the merit in your argument. Wealth that is well over five hundred years old still definitely exists today, having survived and thrived through various disasters. Heck, wealth from land may be thousands of years old and still producing nicely for the rightful heirs of the ancient owners. Wealth managed dynamically has no obvious mode of ceasing to exist, other than the caretaker ceasing to care.
Offenhouse might well have been right about his wealth remaining for all we know - it just doesn't make him opulent any more, as life in luxury has become trivially cheap. Or his caretakers may have ceased to care when they realized the wealth would do nobody any good any more. Or then there indeed was an unpredictable major disaster at some point that robbed Offenhouse of his wealth. But all of these things would be unexpected and unlikely in the mere three centuries he was out of the circulation, considering how stable things have been in the past few thousand years. Or ever since the 1500s, anyway.
What about the starship Enterprise
interiors should give him the hint that his world has collapsed? From what he sees, the United States of America is still going strong and now controls the universe, albeit under funny names and dressing in fashion one would expect of the French. There's nothing really exotic there to suggest otherwise.