Actually I think the reaction would have been similar to the reaction to Benedict's abdication. Actually John Paul II's long terminal illness made people accept that with modern medicine, people can now become ineffective due to aging long before they die. The Catholic Church had already set an age limit on some of the duties of Cardinals, and having Popes abdicate when they started fading was a logical next step.
His successor would still have been Ratzinger/ Benedict XIV so not much would have changed.