[Letang is] a dynamic defenseman and we're obviously going to miss him, but he's hardly the only variable here. We also lost Daley, and had our 4th game in 6 days.
Let's see how we do when we whittle those variables down.
I appreciate the more thoughtful analysis of the game. (Sometimes we are guilty of worthless ad hominem attacks on this forum.)
That said, it is the defense that powers the team bus and it is the offense that drives it.
Back in the Mario days, it was a Paul Coffey (and later a Larry Murphy) who fueled the offensive engine and it was the Mario et al. who drove it home.
I am sure most everyone on this forum has followed hockey closer than I have over the last decade. That said, I have seen a quite a bit of hockey over the last few decades.
Without an offensive D-man such as Letang, a team will have to modify its playing style, resulting in many 2-1 and 3-2 games. This is not exciting hockey, but it might be successful to eke out a few victories (and overtime decisions). This might even get a team into the playoffs. I am not sure, however, if this style of play will be ultimately successful against more offensively minded teams.
Never change Pens organization! 
