I hope you still have it in the Trash and can recover it from there, because it seems to me that you deleted the wrong item, namely the audio engine executable itself. Then Dorico can’t find and start it and therefore reacts with that error message.
Please check following:
In Finder, go to the Dorico application, then right click it and select Show Package Content. Then navigate to Content/Applications. Is there an item VSTAudioEngine?
If not, try to recover from the Trash and if that doesn’t help, you need to reinstall Dorico.
For what I originally meant:
Change to Finder and from the menu select Go > Go To Folder. In the edit box then enter ‘~/Library/Preferences’ and hit return, Finder shall open a new window for you where you can browse that folder. Then delete the contained VSTAudioEngine item.