Actually, we have no way of knowing if this is true. It's an assumption that you're making. In truth, if there are alternate universes out there, there may be one in which Maroney scores and then the Colts go on to put the next 50 points on the board. We'll never know, because the fumble was neither a game ending play nor, as it turned out, a significant game changing play.
The reality is that, after the first half, the score was 24-14 with an entire half to go. The reality is that, after the Brady INT, Manning INT, Maroney fumble, Indy failed drive, Welker return, Patriots touchdown, the score was 31-14 with only 14:18 to go. So, in other words after the Pick/Pick/Fumble/Punt/Return/TD, the lead was larger and the half was more than 50% gone. Neither the Brady interception, nor the Maroney fumble, were contributing to the loss that was to follow. Events following each miscue rendered each of them insignificant.
I'd have no problem with the team bringing in a theoretical upgrade. The team will need to start with the offensive line, though. The most important run blocker starting for the team is seemingly the oldest and most brittle offensive lineman, and the team's decision to go without a fullback is currently looking like yet another mistake in judgment made this past offseason, given the absence of holes opened up by the offensive line.