World wide, I would find having the same condition happening world wide a bit much and slightly annoy.
Unless it was on bomb day. You know the actual day that the bombs dropped.
That would make for an interesting limited play MMO.
Everyone makes and plays a character for the time before the bombs (war). You play business men, construction workers, teachers, etc. Then one day the bombs drop. You are one of the surviors of the bombs and now you must survive your fellow mankind. Good luck.
No Vault people, no mutants, or aliens. Just 3-5 years of actually trying to survive.
Possibly daily random radiation storms, radiation dust storms, trying to find food (or avoid becoming food).
If those were the conditions, then I would not mind as much the (magically produced) entire game world (MMO) suffering realistic conditions.
Dave Chase