From sodrock's posts (and he/she sounds in the know :-) ) I think scenario two sounds unlikely in the near term (some don't even think tL will ever launch :-)). I am not that big of a conspiracy thoerist and think most cases companies want to maximize profits. The back of the hand calc is more than good enough for me so I'll go with your 60% figure, thanks!
I favor the first case. Without making a series of assumptions and running them (I am too lazy to do that) I would venture a guess that MNTA can take 60% of market revenue before SNY would consider launching an AG. The further they take market share beyond that the greater the chance of an AG.
Taking too much of the L market certainly was a factor in the decision of SNY to launch the AG.
Timing suggests that aL approval was the trigger. But with mL up to 59% of the market it was a hair-trigger.