Roche’s purchasing Ophthotech would indeed be a negative for REGN, IMO, but not for the reason you posit (prevention of Fovista use with Eylea, which can’t be accomplished).
Rather, Roche’s purchase of Ophthotech would likely boost Lucentis’ market share at the expense of Eylea by enabling Roche’s ophthalmology salesforce to detail Lucentis and Fovista at the same time.
Note that Roche sells Lucentis only in the US market; in all other countries, NVS has the commercial rights, but the argument presented above remains the same.
Agree that long term Eylea/Fovista should work just as well but if Roche or Novartis buy Ophthotech they can coformulate Fovista&Lucentis and have a unique new product.