As long as their ebitda doesn't decline relative to total liabilities they can buy back stock forever. In the ytd period they spent $1.3 billion on stock buybacks while maintaining ebitda/total liabilities and increasing the dividend.
They could theoretically buy back stock until I'm the only shareholder remaining. I could live with that. More likely, the share price will begin increasing before that happens.
They will borrow to buy back stock until its not longer accretive to EPS. Sooner or later borrowing costs will increase , either by rising interest rates or rating downgrades and the game is over. Domestic cash flow covers the dividend and not much else.