Very fine volcanic ash particles (particularly glass-rich if from an eruption under ice) sucked into a jet engine melt at about 1,100 °C, fusing onto the blades and other parts of the turbine (which operates at about 1,400 °C).
One of the reasons for grounding, ash would not be thick enough for sandblasting.
Clogging of sensors possibly another and electromagnetic wave insulation would be unlikely.
These are the 4 considerations in aviation with a volcanic ash encounter. The ash exists within the troposphere so I don't know how you can fly underneath it.
Decisions would me made on economic as well as safety grounds.