When the trade was reported, it was of note that Elliotte Friedman said it was pending a physical evaluation of JVR's health. While at the time there's no indication that an injury was the reason the trade didn't happen, it's notable this clause was reported.
Regardless, JVR never made sense as a fight in Detroit, being an aging veteran scorer joining a rebuilding team. It's possible that the Red Wings were going to retain salary as a third party broker to send JVR to a contender, but at this point, we may never know what truly happened. In the end, the biggest disappointment is for JVR himself having to finish out the season, and potentially his career, with a basement Flyer's team.