It seems a likely scenario, and one which investigators at the time could have considered, but apparently chose not to, in preference to concentrating all their efforts searching the area between the bicycle and the river.
The bike and supplies dumped at the side of the road were almost certainly left there by some person or persons hoping to mislead search efforts.
Other theories, such as his parking his bike and supplies by the road and then walking to the river only to fall in and drown (and never be found), or being abducted within a 15 minute time frame in the early morning hours by a passing pedophile on a little traveled stretch of road, are rather remote possibilities which stretch the imagination.
IF one of those other scenarios is true, then the boys would have to feel some responsibility for NOT picking Dickie up that morning, or at least leaving him a note to let him know where they were going. Most likely they proceeded to the originally planned hunting area - contrary to their later claims of being 15 miles North of town.
Driving in a car, they would have arrived at the hunting area ahead of Dickie, having a head start and with Dickie riding a bicycle. It is likely that they didn't expect to see Dickie there that morning.
Sunrise would not occur until about 7 am, with perhaps a half hour of twilight preceding it. With various reported estimates of Dickie leaving the house around 5 am, this would place him 4 miles south of town as early as perhaps 5:15 - 5:30 am - a full hour before day light.
We don't know for certain where Dickie and the boys planned to hunt, but Dickie DID know and was very likely headed there to meet up with the others. An early morning hunting accident, followed by hiding of the body and shotgun, finding and staging the bicycle and supplies, and then a made-up story about being well north of town at the time is a scenario well worth considering.
LINK:
weatherspark.com