I suppose the questions should be asked, except that, up here in Canada at least, there is absolutely no need to ask it at all. The answer is already before our eyes. It is present in the Sunday Masses of The Anglicans, the United, the Presbyterians, and other nominally Christian churches that adopted female ministers. It is present in their dwindling congregations and their closed churches. It is before our eyes on the church signs of so many of these churches, which state that there will be but one service every Sunday. It is not the answer they wish to hear, but it is the answer none the less: attendance will collapse.
The question that would follow is 'why?'. Why would people stop attending when this wonderful reform is finally carried out? The answer is not simple, nor is it palatable. Part of the answer would go like this: a congregation is seldom a homogeneous mass. They have different wishes and desires. With an average congregation, some will desire change and to bring the Church more into line with the times, some will desire things to remain the same, and many will not have given the matter much thought. Should this change be made, you stand to lose who want no change very quickly. And the ones who wanted the change... In my experience, they will drop off fairly quickly, too. The change was not extensive enough, or fast enough, or not enough of something. Or they will decide they want something else as well... followed by something else... followed by something else. They will move on. The people who don't give it much thought- well, their feet are halfway out the door to begin with in my experience. Some may stay, but others will drift off before too long, for their own excuses- all different variations of apathy. But surely those who left because of this issue will return. Actually, they won't. Most likely they will have discovered that they enjoy sleeping in on Sundays.
We need to face the fact that those who are demanding the Church change do not want a changed Church. They do not want to Church to have a few modifications. They desire that the Church not be at all.
I sincerely do not know how anyone in Canada can deceive themselves into believing attendance will increase when all the evidence- all of it- points in the opposite direction. One must be capable of incredible self deception to believe otherwise.