I guess you need to use common sense or good airmenship in this case. Finishing Volcanic Ash doesn't make sense without running engines, beside first part that is essentially turning back 180 and putting masks on - exiting polluted area and protecting yourself to be able to proceed.
...loosing both engines has priority.
Even in such extreme case as dual ENG failure, before ECAM, Golden rules are applicable.
Fly, Navigate Communicate will take you out of Volcanic Ash (at least initiate exiting ash area) and as soon as you do that (also first part of Vulcanic Ash check list) you need to jump on dual engine failure.
Fly, Navigate, Communicate before ECAM or QRH shall also include evaluation of obstacles - which is more important than immediately jump on ECAM.