Saint Gasoline speculates about a common idea: using a time machine to travel far in the future to reap the benefits of compound interest. It won’t work!
Lots of bank accounts get abandoned — forgotten, the owner dies, etc., but you don’t have a lot of bankers sitting around fretting, “Uh-oh, Marcus Junius Glabrius deposited 15 denarii in 61 BC, and never closed his account. I sure hope he doesn’t come strolling in tomorrow, or we’ll have to give him Switzerland, France, and a couple of small African nations to cover the interest.” No. That’s because the bankers sit around watching their accounts, and when Marcus doesn’t stop by for a century they say, “Oh ho! That money is mine, now!” Either that or the next regime sweeps in, confiscates all the money and sets fire to the records, and uses the bank building to quarter their horses or mistresses.
St. G regrets that his plan has the unfortunate glitch that while he is a billionaire, he has to live under the tentacles of the giant squid overlords. This is of no concern. When the squid overlords see St. G, they don’t see a banking customer: they see a pleasing sample of mushi (it’s like sushi, only it’s from the future, and it uses mammal meat and doesn’t bother with the rice and seaweed. Or the little cups of sake. Or table manners.)