Nate;
I've "saved" some really old rubber hackle before, by pouring out enough Armoral, into a cup and soaking the hackle in it. Usually, overnight. Then, used the water trick.
Armoral is water based so it washes right out of the rubber hackles, no problem when they're dipped into the boiling water.
DON'T use, something like "STP Son Of A Gun" brand of vinyl treatment, as it's OIL based and will ruin the hackle. (oil rots rubber).
Of course, this whole thing really depends on "what is this particular hackle, WORTH, as to how much trouble you want to go thru' to save it!?!