I still think there's a possibility that someone stole his bike
I went from Tyndrum to Bridge of Orchy last week and the river was very shallow in most places, due to the continuous dry days/warm weather, with just rocks at the bottom showing. I also went through Glen Orchy a little and the river looked mainly the same there. I don't know if the river is usually deeper through there as it's been about a year since I last went that way. So you'd think that if the rivers go down a lot with the warmer weather, then he might just be spotted this summer by one of the tourists...fingers crossed.
There's also another far fetched possibility that he might have passed the CCTV at Tyndrum without being noticed because he looked different. Maybe he might have ditched the bike if it became damaged or might have got his bike muddied up so it looked brown instead of yellow or he changed in to some other clothes as his first outfit got too wet to ride in so passed the CCTV looking like another person. I'm just trying to think how an investigator might think (and probably watched too much TV lol).