I am nervous of company buy back programs that are financed by debt for the following reasons
1 Increasing debt can't go on forever (as you mentioned)
2 The perverse incentives it creates.
Many companies pay bonuses according to their share prices performance . If the share price goes up the employees get more money. Share buy backs add to the demand and decreases supply of shares therefore increasing the price. This creates an extra expense for bonus payments which comes at the cost of long term viability of the organisation as the money wasn't used to improve the company's situation
The perverse incentives encourage a fragile company with high debt and low capital reserves.

Of coarse each company should be judged on its own merits but a company doing buybacks with debt isn't a positive long term sign generally.
Thanks for the article