Cattle not pets. Carve a new partition with gparted, install new OS, mount the old partition and copy over any valuable data. (Hopefully you have this backed up anyway)
Or, if you really want to get into the weeds, try to re-install systemd. As a learning exercise.
This is a great question on a job interview though. "What happens on a Debian machine if you 'apt remove systemd'?"
I've been a unix and linux jackofall since '96 or so, and I could not answer that question better than "probably a big mess"
Though it would certainly not be points against if they did happen to say "I tried that once just to see". That is good curiosity and tinkering, but I never happened to try it once just to see myself.
I guess it could be a valid question just to see if the response shows some flavor of shock and alarm. IE everyone is expected to say "I don't know" but if the response is blank as though the question were not remarkable, that's not encouraging.
I guess my answer would be "Holy sh... we don't have time for this, take me to the machine right now." haha Or just "I dunno but I'll clean it up."