Presumably it would be an ownership group like e.g. Tim Cook + some other people borrowing the money, and/or they'd partner with a P/E firm. Isn't that what Dell did a couple of years ago?
Sure. If Tim Cook and "some other people" could borrow 600 billion dollars, they could buy Apple. Turns out that it's really hard to get a loan for that amount though.
And regardless this has nothing to do with Apple running a stock buyback.
And regardless this has nothing to do with Apple running a stock buyback.