You assume all no voters are non strikers. I suppose from the companies perspective the glass is hall full looking at it this way and so that's what they told the press and customers, they wouldnt want to scare people.
Just for one second assume the glass is half empty, then only 12% of union crew are willing to operate plus non members who are not sick (lets not argue on the sick thing, we know there will be huge sickness these days, maybe as high as Christmas >400)
In reality we dont know what the "non voters" will do.
They cant change someones roster, they could of catered for it if the strike dates had been released pre roster issue but they were not, I dont know of anyone who has has had a roster changes to cater for strikes.
If the company has planned it can operate because only 30% of crew will strike then there will be a rude awakening. It would stand to reason that the company perhaps believes it is more than 30% who will not appear to work, could that be why it has offered incentives to bribe people to come to work, otherwise there would be nothing to worry about would there if 70% of crew were coming to work?