In the United States, I believe it is illegal to "fire" employees who are legally striking, but they can be replaced. If the strike is due to non economic reason, the striking employee will immediately get their position back once the strike is over with. If the strike is for economic reason only, the striking employee will get their position back when positions become available. Whether the strike is or isn't for economic reason, the employee can be denied returning if they they did anything like prevent the scabs from working eg blocking them as they attempted to enter the work place, made threats, etc.