An update - we decided to try & get through to Emirates on the phone. After hanging on for over an hour I got through. The guy was really helpful. He told us that the London > Dubai flight was still going ahead but the Dubai > Perth was not. The London > Dubai was supposed to be for UAE nationals & residents only but he could get us onto it if we would accept a re-route to Sydney which we declined. None of this was obvious from the info on their website but I can't fault the operator (shout out to Shade!) 

The upshot is we are now checked in to our Malaysia Airlines flight!