I think it depends because Robert was excellent at not turning the ball over. If Kirk played 16 games and had 10 or less INTs and 6 or less fumbles, then I would say: Yes, we are a playoff team with Kirk. I think we would have been a playoff team in 2011 with Rex if he didn't throw 1 INT and fumble 1 time in almost every game.
Our offense is good and is able to move the ball on the ground and in the air. With Robert, it is very dynamic. With Kirk, it would be a little more predictable, but if they take care of the ball, they will be able to move it and score some points.
I just had 1 more thought - With Robert we were so good in the red zone. Even without turnovers, there could be a dramatic drop off from Robert to Kirk in this area of the field.
All this is moot, since Robert will be back by late July. The down time will allow him even more time to study the game!!!