During peace talks with Olmert Assad said that the location of remains Eli Cohens were unknown which sadly I think is probably true.
Assuming Assad does know where they are why would he return them, we still have the Golan, we are his enemy, we have been carrying out bombing raids over his country.
Eli Cohens actions were also a humiliation to the Syrians and is partly responsible for the fact we have the Golan today because he gave the IDF Syrian military positions by getting the Syrian government to plant trees at military locations on the grounds the soldiers have shade and so the IDF knew where they saw these trees there would be Syrian soldiers.

I remember his capture and murder well .An eternal hero.We were hoping that he would be exchanged. Good to see his widow well at 83

It may not have been wise to choose a hospital that treated Assad's sworn islamist enemies as a place to ask him for a gesture of good will. But Bashar may still have sympathy for Eli's widow and return the remains to her... even if it places him personally in a dangerous position (many in his entourage may not be too happy about such a gesture, especially right now with already difficult Syrian-Israeli relations at an all times low). May humanism prevail.