I think Langsdorf is a good QB coach/position coach. But, from what I saw this year, his OC capabilities are severely lacking and not real desirable. If the choices are he stays and calls the plays/offense or he leaves, I would rather see him leave. The play calling and type of offense he (and Riley) want to run does not appear to be anything we should want long term. Lots of people have speculated that we could've won 3 or 4 more games if TA had played better, and I would agree with that but, I would also say we could've won 3 or 4 more games if Riley and Langs had sent in more sensible plays at critical times. When your OC is in charge of sending in the plays and he is afraid to run the ball on 2nd & 1 or 3rd &1, in a 4 down situation, then personally he can't leave soon enough for my tastes.
The only thing I'd add to this is that Langsdorf knew what he had with Tommy coming in--there's two years of tape on the man under center at DoNU. If you can't call plays that accentuate the positive and align with Tommy's strengths, then you're just as much at fault, if not more so, than the QB on the field that didn't make the play.
But yeah, JJ is dead on, and I know many of us have said similar things in game threads, and if Langsdorf stays on as a QB coach, we could roll up Special Teams to someone else--it's not like having a specialized Special Teams coach paid dividends this season...