As far as I'm aware OpenStreetMap users still have permission to make use of the Strava heatmap data (osm.wiki/Permissions/Strava).

As regarding the accuracy of the paths previously mapped, I walk and run in the path plenty, and know of many marked paths which have no longer or have never existed. I will endeavor to use my own GPS traces to mark out those which may not be covered by the heatmap.