The number one job of an engineering consultant is to recommend more work. I never saw a consultant report that didn't do this. In this case, they got a fat 'no bid' contract to do some more drilling.
Although this dam may slump a bit in an earthquake, there is no giant wall of water, just over-topping, and slow erosion. Is this serious when all the buildings have collapsed? I suppose it would affect rescue work, but I'm sure all the damage would have been done in the main event.
So, there is going to be more drilling.