I do not think that shoving one subway car out of the way, parked under the wide open sky, and that would create extra work to extricate, would make for a compelling example of preservation. As well, keeping only one car would mean that they'd be unable to move themselves under their own power for any reason whatsoever, which would mean even more work. If the general public can't easily get to it, what is the point of keeping it around?
The abandoned H4s from Wilson are not parked at Greenwood, and were carted off to scrap in November 2012. The H4s which are parked at Greenwood are either awaiting conversion to work cars, or serving as parts donors for work cars.