Not really possible for a bee with both EHB genes and AHB genes to become 100% pure AHB. Once the gene pool is contaminated, isn't it then impossible to purify it again?
Once a hybrid, always a hybrid. Backcrossing to either parent line should increase the genetic influence of the parent line used, and reduce the genetic influence of the other parent line, but will never eliminate all of the genetic components of the other initial parent line.
I am also curious about the hypothetical reproductive advantage.
Supposedly AHB drones are more likely to be the drones that mate with any available virgin queens.
I've also heard that AHB and EHB drones and virgin queens have different schedules, so that AHB drones aren't available for EHB virgin queens and the reciprocal.