More points, some in favor of Robin:

The probability of losing your money each year is likely not independent. If you've managed to last the past 11,000 years, it's relatively more likely you'll last another 1,000.

Also, if the expected gain year-on-year is positive (for example, if our assets grow by a factor of 1.02 every year, and there's a .99 chance that they continue to exist, that means their expected year-on-year growth is a factor of 1.0098), then the argument could still work. But you start getting in to Pascal's Mugging territory there.

Another point is the implausibility of economic growth continuing for that long. Things don't grow exponentially in nature forever. Typically they reach some carrying capacity, run out of resources, etc.

Overall I think Robin's idea has a low enough probability of working that it runs in to Pascal's Mugging territory, but it might be worth doing with a small fraction of available altruistic resources.