You're not going to hire a replacement worker unless you're on strike. You're going to hire a contractor to do this job 12 months of the year. There is the difference.
A replacement worker is going to be called in to do my job, while I'm out striking on the picket line. Things continue to go, to move. The difference between a replacement worker and a contractor is that with that contractor, I'm never going to get that job back. The strike is over. Hopefully, I'm going to be able to go back to my job, and that replacement worker will be gone. However, if you bring in a contractor to take my job, I'm never getting that job back.