Sorry to hear this. Had a few close calls with my Spaniel after it bolted after hares/deer.
The technique we always used to find it if it did run off for extended periods of time (3 or 4 times during her lifetime, She’d only ever run off if she wasn’t entertained by you playing fetching/retrieving games with her.) was to stay out for several hours with one or two people calling from a single spot (last place the dog saw us) whilst another zig zagged a few square miles of the country side.
It always worked, however once she bolted when she became deaf. We were lucky that time because some motorcrossers spotted her.
The next Spaniel I have will have a gps unit attached to it’s back.