What are the rules around closing Catholic churches that are part of restructured parishes?

Our diocese is doing a rather major restructuring and the church in my small town is being joined to a larger parish. We've heard that the diocese cannot sell off churches unless "the congregation" wants them to. So, if we're being swallowed up into a parish with five other churches, what's to stop those five churches from making a practical business decision to sell off our Church? Or, to be more direct, who represents the congregation once the parish is reorganized?