What we have been told is that this is a loan preceding an obligation to buy. In other words we've to all extents and purposes bought him, with the loan being a technicality whose reasons have been discussed. And no sale of players ever have come with a money-back warranty. The only strings ever attached with player sales are add-ons (number of appearances, etc.), which would only save us a small percentage of the fee if he blows out a knee in the next year or later.
It's possible that the obligation to buy at the end of the loan has some injury get out clause for Saints, but why would they keep this secret?