Just for added perspective, The Lamb pub, Elephant and Castle pub - they look quite close on the map, but Lewes is extremely hilly. Downhill from the pubs = Waitrose, and the river is down that way too. If he did wander that way, it would be easy for him to get lost coming back, and all uphill, which could be tiring after a day of drinking.
I'm so sad to hear that the local police have called off their search. As another poster mentioned, perhaps when normality returns tomorrow and people head back to work after the holidays, an answer may be found.