It would be better to tear them down.
Here in my NE town, that used to have a lot of immigrant Poles, Irish, Germans and Italians, we have a lot of closed Catholic churches. Most sit, boarded up, while the diocese tries to sell the land, find other uses, politicians compete and complain, etc...
There was one though, in the what is now the Yemeni-immigrant section of town, that closed about 5 years ago.
The church and all buildings were razed within about 2 months of the closure. No announcements, just one day - gone.
I think I know what the Bishop was thinking.
...and sow the ground with salt.
I can't argue with that. I'd be loath to give up the value of the property by destroying it, but yours is an understandable alternative.