When towing gliders there is a weak link in the tow rope at the tug end if it is a fixed hook rather than a winch. It is there to protect the tug if the rope gets caught on anything. A weak link at the glider end may also be used but in my experience usually isn’t. I can’t see that the link used for banner towing could be any stronger. I don’t have the Pawnee TCDS to hand but I imagine that the link would be specified to be no stronger than 600 daN or about 600 kg - probably less.

Another one, fortunately not fatal, from the same operator:
https://aviation-safety.net/wikibase/313746

Yikes - this operator is becoming the new 'twenty minuters'... looks like the FAA need to get busy