Include the corners of the sail in your pinning group (possibly with a lower weight, depending on how rigid you want the attachment to the rope to be); at each corner add a hook to a new empty; and vertex parent each of those empties to the appropriate rope end. The sail corners will now be dragged by the rope ends.
Next do the same thing the other way round: at the end of each rope add a hook to a new empty, and vertex parent those to the sail corners. The rope ends will now be pulled by the sail corners.
I got this to work OK using cloth for the ropes as well as for the sail. I’d rather have the ropes as soft bodies, but I couldn’t get softbody ropes to follow the sail corners as cleanly. That may just be because I’m much more familiar with the cloth settings than with the softbody ones.