You're saying that your program is already as effective as your team in the majority of cases. I've done my fair share of automation, and very often people underestimate the amount of work required to bring a script to the level of an human (which is normal! You're the person who wrote the script after all). Your script is most likely going to be 30% to 50% as productive as a normal person, at least in the beginning.
Another thing to keep in mind is that there's a lot of work that can't be automated. These people may have domain-specific knowledge that you don't have. Very often domain experts take decisions which look like guesses but aren't.
What I would do in your place would be to redesign your program to be a tool to supplement humans. You could sell it as such to your higher-ups, and help some of those people keep their jobs.
Also note that it's somewhat unlikely to have a massive lay-off happen. Most people will get reaffected to another role or a slightly different mission. Managers don't like shrinking headcount.
Finally, don't forget to take credit for this. You've been toiling on this for months after all, on your own. You deserve credit for it.