At this point the launch is a very positive move for Momenta.
How it plays out from is a little sketchy but it should be in Momenta's favor (proving that once again the recent ATM's and Stock sales were a massive mistake. The CFO should be given his walking papers).
With Mylan not receiving FDA approval yet is extremely positive and I expect TEVA to take them out prior to Approval. That will mean that Natco will lose it's sponsor and will delay the approval further.
I do expect the FDA to approve someone else in the long term and then Momenta will be back on first base, but as of now it's party on time.