Our containment efforts could prevent any significant self-sustaining communities in the USA. This seems plausible.
Testing could advance to a point where Apple safely and effectively door tests attendees. This seems like something Apple would and will do, if they can (e.g. if testing advances far enough in the next month or so).
I think Apple will announce a decision between 30-15 days out from the event and by that time their choice will be an obvious one.