From my understanding your strata is stuffed as the origional owner who made the illegal change has gone and now the reasponsibility for removed wall falls on the Strata not the new owner.
One soloution would be to approach the owner asking him to accept reasponsibility for the alteration (and add a bylaw stating that) or the strata will return the units to their origional config ie rebuild the wall at stratas cost.
He might accept the status quo by accepting reasponsibilty for the alteration if he wants to keep it as a single appartment.
BUT has the removed wall affected the structual integraty of the strata building.