In essence, replay would be reviewing two reviewable plays, targeting, and an incomplete pass and trying to determine what happened first.
I've seen replay take action on a targeting penalty that was ruled on the field to occur after an interception. Team B was given possession, with the foul marked off after the change of possession.
Replay confirmed targeting, and determined the foul clearly occurred prior to the change of possession. It was obvious, easy to see at full speed. Team A keeps the ball, 15 yards from the previous spot. This was very late in a 1 score game, with Mike Defee as the white hat.
I'd think, especially in that 4th down case which would have resulted in a change of possession, replay could take a closer look as to whether the foul occurred after the ball hit the ground. This would be that obvious error that may have a significant impact on the outcome of the game.