Theoretically it is possible to form a new gov even if less than 151 seats are secured. All it needs is a big party (ND) to give a confidence vote. Of course the gov could fall at any given time but if IMF, EU and co push enough a re-election would not be acceptable so one way or another a new gov will be formed just to pass more austerity measures.
The risk in this scenario is - for them - that when a new election comes, left wing SYRIZA might be able to win 1st place this time.