Wouldn't sending those coins as a(possibly huge) fee be a better approach? That way, those coins get back to the miners and not sent into oblivion to a valid, but onowned, address.
That wouldn't be destroyed.
There is no actual way of "destroying coins". Even sending to an address with a private key that isn't known, a person can also get a lot (and i mean a real lot) amount of hashpower to bruteforce the key. Although it would be difficult, the coins are still recoverable.
no, not really. what deathandtaxes said still applies. it's computationally unfeasible to the point that it's hard to comprehend.