Back to Church Sunday is a neat idea. There really are people out there who would consider coming to church if asked. Churchgoers get to interact with their unchurched or de-churched friends without having to talk about anything difficult like God, or their own personal faith - it's just a question of making the invitation. But there are one or two cautions to considered before investing Back to Church with the "essential" label, and seeing it as the panacea for all the church's ills.
The most obvious one is the question of what you are inviting people to come back to. There are all kinds of reasons why people don't go to church, or stop going. Unbelief or disinterest is only part of the story. In many cases it is painful experiences, unsympathetic rhetoric, irrelevance or just plain boredom that has driven them away. Unfortunately in the case of many of our churches there is a real risk that these people will return, only to find that nothing has changed. Of course the temptation is for churches to put on a special show that will convince the newcomer that this is the most lively/friendly/relevant church in the neighbourhood, but if this is just a whitewash, then it merely postpones the disappointment by a week. The question of what prompts people not just to come to church, but to stay, is very complex and a one-off invitation doesn't really address it at all.
"Back to Church" is no cure-all. But it would be very effective for churches that are actively trying to change to a more outward-looking way of doing things, used as part of a programme of outreach. That way, visitors will arrive at a church that is already set up for welcoming newcomers, and will be treated not just as exciting curiosities ("look, somebody different") but as potential new members of the community.