Depends on the jurisdiction. In the US, each state has escheatment[0] laws governing how untouched accounts are retired and how they may be subsequently claimed by their original owner. That process typically happens through a government agency rather than through the original company that held the account. But other parts of the world have other processes.

[0] https://en.wikipedia.org/wiki/Escheat#Transfer_agents_and_es...

That doesn't seem logically related (though that doesn't mean it legally isn't). If there's a statement from last year saying that the account has x amount of money in it, then that's a document within the 10 year retention even if the last deposit was more than 10 years ago, so there's still a record that the account exists.

Yes? What happens if you don’t ping in 20, 50, 100 years? At some point between 0 and infinity, it’s probably safe to assume you’re not coming back.

You can argue where to draw the line, but arguing that there shouldn’t be a line at all is absurd