I believe the old whalers in their long boats carried a hatchet to cut the harpoon line if they needed.
Note to self get a hatchet for the emergency kit!!! olewilll
Read "Harpoon at a Venture" by Gavin Maxwell, the story of his attempt with Tex Geddes to set up a shark oil fishery in the Scottish Islands by harppooning basking sharks or any book about the Azores whale fishers. It's the way it has been done for centuries.
Tho I must admit it's unusual for a whale to take a rope in its mouth & pass it on to a pal - much more likely to have accidentally entangled & another has come to its aid & got entangled itself.