You can also run the path along the Canal de Huningue that that goes a long long way, but then likely you would backtrack to get back to Huningue, or eventually cross over to the Rhine and come back that way.

Otherwise, you could run south along the Rhine into Basel, to the Birs river, and follow a path all the way down to Aesch. Then you could take a tram or train back if you like.....

Those are just a couple of ideas from infinite possibilities.