Eat it cause it sounds like it will rot. If it still looks shiny and the skin is easily pierced with your fingernail it won't continue to ripen off the vine, sorry.

Here's what you can do, if you realize you didn't give your butternuts enough time to ripen... (MIGHT work for pumpkins too!)

1) Put paper towel down on your window sill.

2) Place your squash "stem up" so they sit nicely and can get enough sun.

3) Take additional paper towel (about 1 piece for every stem you have), wet it, and wrap it around the cut-off stem. Try to do this as soon as possible after cutting your squash off the vine. Also make sure most of the paper towel is where the stem is cut off.

4) To make sure it stays damp, take a piece of foil (I used pieces about 3-4" squared) and gently place it on top of the paper towel that is covering the stem of the butternut...making sure to pinch it tightly around the part of the stem that is closest to the fruit (so the foil should resemble the shape of a light bulb). Make sure the foil completely covers the paper towel.

5) Repeat every day, for about a week (or less if your stems happen to get mushy, mine didn't), to ensure they're getting enough water to keep them ripening.

TAH DAAAAAAAAAAH! Brilliance at it's best.

Thank you.
(I made this up, and tried it, and it completely works!)