The words were reiterated a few days ago, but are just words:
"No we continue to cover the default of traders. Hence our changes to ensure no default happens" (
http://www.reddit.com/r/BitcoinMarkets/comments/2akrbp/psa_bfx_is_making_some_changes_to_margin_trading/ciw69d5).
In the end, the guaranty against default is reversing trades.
But if there were defaults, despite a reversal of trades, and they didn't honored this promise, they would have problems to stay in business. The damaged to their reputation would be heavy.
Therefore, in face of the losses, they will balance what is best: to pay and keep in business; or, end the business and run away.
If I recall well, it was in April 2013, because of the crash and connection problems with Gox, since it wasn't possible to liquidate positions, they end up paying the lenders losses, even without any promise in that sense. Of course, it was a relatively small value. Now we are talking about millions of potential losses.