Nobody knows how long he will keep doing it,all we can go on is that he has gave no indication it's likely to stop soon and he is not putting the club at risk because he just converts the debt into shares.
What Sunderland are doing is no different to what Chelsea and Man City are doing(smaller scale obviously) in that they are being bank rolled by billionaires and if they stop putting the cash in then the buying stops immediately.
Incedentially how Newcastle were worried when the Halls and Shepherds were doing exactly the same at Newcastle?seems like sour grapes to me.
I'm sure Short will come to his senses and realise he's more chance of catching diarrhea in his hands than making a profit on blunderland.