Don't think there is any default so far on insured or non-insured lending. The last time BTC crashed from 266 to 66 because of ddos attack on Mtgox, they pay out the default loan to the lenders  from their own pocket.


The risk of default is actually pretty high right now, as people borrowing irrationally to buy coin. Anyone using max leverage will get wipe out with 25% price swing. And we see this kind of price movement every day for the last 2 weeks now.