Considering the importance allardyce puts on defence and work off the ball I think it's fair to say he will consider keeping Kenny in.
He'd be silly not to.
Then you are, in fact, suggesting otherwise. And you are, like we all have before when evaluating young players, undervaluing Coleman and overvaluing Kenny. The same thing happened in the cases of Oviedo, Garbutt, and Galloway when Baines had to miss games in the past, and with Holgate when Coleman missed games in the past.
I actually do think that Kenny is a better prospect than Oviedo, Garbutt, Galloway, or Holgate (at outside back). But you are making pretty huge claims based off of Kenny's very small sample size of work. And seemingly forgetting how great Coleman is (both going forward and on the defensive side of the ball). Otherwise, I can't see how you could justify your pretty crazy suggestion that Big Sam will actually hesitate to play Coleman (one of the top 3 RBs in the prem over the last 5+ years) over Kenny (a 20-year old with around 12 starts to his name).