At present no one to my knowledge knows enough to satisfy themselves that the risk is manageable. Failure to manage that risk could involve loss of life or grounding a large chunk of the fleet in the coming weeks/months due to lack of engines.
Of course we do, it just takes a little time and data to sort it out to the satisfaction of the operators and the authorities.
The risk managers define the data necessary and the authorities examine the numbers to ensure that they do not appreciably increase risk compared to the normal base risk that is carried in day to day operations. No doubt it may take some extra precautions for the time period that the risk of encounter is raised (operation downstream of an eruption) as well as increased maintainence actions between flights.