If you deleted the mods by unsubscribing on Steam:
Did you disable the mods in-game before deleting them? If you didn't, keep CTRL pressed while launching Banished in order to bring up the options before the game itself, and tick "Disable all mods", then launch.

If that doesn't help, go to your Documents/Banished/Saves folder and move out the saved files. It's possible that the game detect that all your games were using mods and gets confused without them.

If you deleted the mods manually by cleaning your mods folder and the previous stuff still doesn't help, go to the mods folder (Steam/Steamapps/common/Banished/Windata) and check that you still have the data0.pkg, data1.pkg, patch0.pkg and patch1.pkg files in there. Those aren't mods, they're required by the game to run.
If they're missing, you'll either need to tell Steam to Verify the game integrity (right click on game in your library, Properties, Local Files tab) or to get your installer back from GoG or wherever and reinstall to get those 4 files back.