Interesting that even then, it doesn't say "he was seen pedaling away...".
Just to think through the possibility of Dickie's demise being the morning or even day after the tavern...did each of Dickie's parents have a car? If they did, I wonder if one or both had blood stains from hunting, which might be normal in that community. As well as morbidly lucky before forensic testing.
I recall an eariler mention of the road, from someone familiar with it, that it was unlikely Dickie would have tried it on a bike in the dark. But I posit he might if he was desperate to get away. No way to know if witnesses would be around at civil dawn, certainly other hunters en route to wherever; but there is still the issue of the boys coming to the house, which the parents allegedly knew was happening. A risky timeline in the morning, so I'm back to whatever happened being the night before, and the parents just didn't answer the door in the morning. So...perhaps Dickie left the night before to escape a beating (saved for behind closed doors upon return from the tavern)? All I can say is stars were brighter then (and there), with a half moon on that date - he might have taken off the fastest way he could. Probably intending to stay away until his father sobered up; this could have been a pattern, or at least happened before.
Anyway, fleeing that night would explain an easier ride because he wouldn't have been juggling his gun, lunch or supplies. Maybe he made it to where the bike was found and hauled back home, or was intercepted in the driveway and the bike placed later. Either way, I'd like to know if the father routinely had the gun in his vehicle, or if it was easily accessed by door, etc. Somewhere there are statistics on the likelihood of a parent shooting their child. But revisiting the blackout, who knows. It's just as likely it was wielded as a threat to scare Dickie and went off accidently, or didn't fire but was wielded as a blow and cracked his skull. Both scenarios would explain getting rid of it, if not for evidentiary reasons than at least sheer horror and shock. That same shock and adrenaline would be in play while collecting his hunting outfit, grabbing shells, etc. to place with the bike.
If that weren't awful enough, it's also possible he didn't die right away. He might have been kept elsewhere on the property with a head injury, unconcious or non-communicative. There'd be a lot of questions taking him to the hospital, even without the father showing signs of intoxication or a hangover. If Dickie succumbed to brain swelling within hours, or bled to death on the front lawn, the same outcome of him still being on the property holds. It would also keep evidence out of the car/s and away from the bike.
The detail about the large amount of food for his lunch sticks with me. In 1965, I'd guess his mother typically made it. So a couple of reasons why it would be excessive that day: she made enough for the other boys, shock/denial/guilt led her to make it extra big for her dead son, OR she didn't make it....the father did, and made it father-size rather than Dickie-sized.