No argument within the context you are considering, but let us think of the case of an at-risk launch followed by an MNTA court win. In this case, after aL is pulled, NVS will very possibly be making greater profits due to the contract not reverting.
So in this case MNTA would be better off suing on their own as the Court could not possibly divide an award with a negative amount going to NVS.
Of course I kind of suspect that they might have agreed to terms with each other already on this.