Unfortunately, given shale wells will continue to produce even when the companies that own them go into adminstration (or get taken over), oil supply is unlikely to fall of a cliff, only ongoing investment. The Saudis might even try to increase supply for a few more months to deliver the killing blow. Last thing they'll want is oil spiking again when creditor renogotiations are happening with banks in the US.
But given the Oct 1 deadline is well known to both private and government players, I don't expect wider market turmoil (I hope) caused by defaults in the shale sector.
Having said that, very happy to be holding DLS for the long-term, just think picking a bottom for oil might be more tricky than the shale crash story - which is very real - might indicate.