OP:
Yes, you can "go back" if you really want.
But without a bootable cloned backup (created with either CarbonCopyCloner or SuperDuper),
that's going to be a "long, hard journey".
What you'll probably need to do:
1. Download either CCC or SD.
2. Use either one to create a cloned backup of the Mojave install. Disconnect this and put it aside -- you'll need it later on.
3. You'll need a copy of the High Sierra installer. Get it here:
https://itunes.apple.com/us/app/macos-high-sierra/id1246284741?ls=1&mt=12
Download the HS installer but DO NOT RUN IT yet. Just leave it in your applications folder (where I believe it will download to).
4. You'll need a USB flashdrive 16gb or larger. ERASE it to Mac OS extended with journaling enabled
5. You'll need DiskMaker X. Get it here:
http://diskmakerx.com/downloads/DiskMaker_X_701.dmg
6. Use DiskMaker X to install a bootable copy of the High Sierra installer onto the USB flashdrive. This can be done with a very few clicks of the mouse.
7. Now boot from the USB flashdrive installer (press power on button and IMMEDIATELY hold down the option key and KEEP HOLDING IT DOWN until the startup manager appears -- you can select the USB drive and hit return)
8. When you get to the installer, QUIT IT and go to Disk Utility instead.
9. ERASE the internal drive to Mac OS extended with journaling enabled, GUID partition format.
10. Now quit DU and re-open the OS installer.
11. Install High Sierra onto the internal drive. This may involve one or more reboots and will take some time. BE PATIENT.
12. When the install is done, you'll see the setup screen.
What I would attempt at this point is to connect the backup and see if migration assistant will permit you to migrate ONLY your user folders and [maybe] settings. I don't know if you can migrate apps from a backup that has newer version of the OS than your "target" drive.
If this doesn't work, you'll have to do a "manual migration and reconstruction".
See what I said about a "long, hard journey"?
This is what happens when you do a system software upgrade without a bootable cloned backup.
Go forth from this day, a sadder and wiser user, and learn!
Final thought:
If you don't want to do the above, and you can't get the old printers to work, then perhaps the easiest "way forward" is to start shopping for a new printer...