Lets imagine there was actually huge amount of them - 90% of passengers. Just to make very obvious to see.
That means that company has 90% less revenue to operate with and operate costs.
They could cancel enough lines to stay in positive numbers. Now the cost for everyone is that service is way worse.
They could raise up fare. Paying 10 times the fare is quire a cost raise for paying people.
Or they could lobby local government for tax subsidies. That would come in greater taxes or tax money missing elsewhere. Raised costs for everyone, even people not using public transport.
Of course, company could just shut down. Id say that is quite a cost.