There is another thread where a US resident describes how a Swiss PostFinance account was opened.

I disagree. Opening a bank account takes only a few minutes, provided you have a valid ID with you, and provided you are not a "yankee" trying to open an account at UBS

What about leaving an account open upon leaving CH? Anybody know the rules for that? Is it allowed, or must an account be closed once you terminate your residency?

Of course you can keep a bank account.

I just recently closed all my accounts at UBS, I thought they would asked any question like why do you want to close this account, but they didn't. It was really easy took 5 min and didn't cost anything.
About your account form the deposit, that should have no influence and you can keep it, you don't have to pay anything for this either.

Why not go into any UBS bank and ask what it cost to close an account?
If they ask for your account just say that you're not a current customer and you would just like to know what the costs are for terminating accounts?
Why do you even need to give them your info? Just ask.

I'd leave it open, only to be able to say that I have money on a Swiss bank acount, which sounds really bad-ass

Closing a UBS account is one of the easiest things possible in CH. I did it a few years when I opened a Kantonal Bank account transeferred everything contacted them and closed it and the girl that was helping counld not have been more helpful.

Usually only need to give them written notice and simply as