A chiddush not Halacha Li-myseh.
The Oneg Yom Tov says that if one is a dangerously ill person and eats matza against the doctors orders - he is not yotzei [and has to eat again if he gets better in time]. [See also ציץ אליעזר י"ב מ"ג]
I would suggest that if one davens in a minyan that was forbidden by the doctors and rabbonim - he is not yotzei and has to daven again [this time alone].
