A jigsaw with a carbide blade won't do much on case hardened steel. If it scratches it it will just seize the blade at any depth, too flexy a setup to cut that.
You will have better luck with a cutting disk on your power drill, buy two, channel your cut to be wider than the disk. If your drill is low rpms it will just take longer.
Bolt cutters that can cut that chain are 6 foot long, I guess you could use smaller ones with cheater bars but you still need to be able to put several hundred pounds or pressure at the handle end of the cutters and be able to brace against the ground.