My understanding is that they do another identical trial to BETOnMACE.  The # of patient years would be obvious from statistical extrapolation of the results so far.  Let's say they need another 50 MACE events.  That would probably imply 1000 patient years (a fifth of the 5,000 patient years I am guessing transpired for BETOnMACE).  They can run it with 2,000 patients for say 18 months just to be on the safe side.

Note that the hardest problem for such trials is recruiting patients.  Now that the drug has been shown to be "safe enough for chronic drug use", getting such patients on board would be very quick.  

In short, if the FDA accepts Option 2 (smaller bolt on trial), then you are pretty much assured of a billion dollar drug in 2 to 3 years time.