unions

When it comes to hospitals the strikes are scheduled and the hospital is required to hire strike nurses until the strike is over because legally they can't just not have nurses. Strike nurses are just travel nurses but to work durring a strike they generally charge several times what a regular nurse gets paid and the hospital doesn't get a choice because they need nurses. My mom used to be a travel nurse and I remember that when working as a strike nurse she often made over $1000 per day plus travel expenses and housing paid for. I think the most she ever made was $2800 in a single work shift but that was at a hospital in a fairly wealthy area.

So yes hospitals do just hire other nurses to cover the strike but they usually don't want to do that for long because it's incredibly expensive compared to just caving to the strike demands.