I agree with most of what you said except this. Sarah answered to me that their 250 target events were adjudicated events so dosing stops there and it is announced. Adjudication does not stop there as they will complete the ones in progress (Pile #2) and move the confirmed ones to Pile #3. That is where we can arrive at the possible 270 or whatever as they mentioned. To answer your query in paragraph two, "Do they go back to taking the drug/placebo?",  they probably never stopped dosing. The main thing here though is that dosing stops at 250 adj. and followups can probably start for at least those in Pile #3 but probably all as they are no longer being dosed. 

You are assuming that when an event occurs, the patient stops dosing. RVX has stated that all patients will dose until end of trial (except unfortunately the deceased). I have also heard it posited that someone might have two events but the second is meaningless to trial stats as it is time to first event. Even though your three group idea is correct, my belief is they will all still be dosed all the way to 250 adj. MACE events.