Culture Secretary Andy Burnham has suggested that poorly attended church buildings be turned into gymns, restaurants etc. in order to protect them as heritage sites. (Ht Dave Walker) Personally I'd love to see gymns and restaurants turned into churches. Just imagine being part of a church which met over a curry, or doing your Pilates with Tallis playing in the background.
What kind of exercises would a church/gym have? We have a fairly good selection of warm up exercises (raising hand, lowering them, standing and sitting on order, genuflecting, sharing the peace, and perhaps a longer and slightly faster procession than usual as a cardio warm-up), a few trips up and down the tower steps would do the job of a stepper, and hardback hymnbooks could take the place of weights. For the really committed you could bench-press a pew.
The really innovative thing would be for churches to do this (I'm being a bit more serious now) as a mission initiative, not simply as a way of saving an old and lovely building. Remember that church is not a building, neither is it an event put on in that building on a Sunday morning (though we often confuse people by saying 'welcome to our church' at that event). The church is the community of disciples in one place with a common love for God, one another, and a common mission to make Christ known. The building is an asset to this, but it doesn't define the church.
The great stones may not be left upon one another (Matthew 24, Sunday's reading), but that doesn't mean God has left town, it may just be the beginnings of birth pangs, something new, something gospel.