In a word... no. They will not ripen further. Neither will they be bitter. But they likely won't have the rich, sweet flavor you'd expect from a Butternut. Butternuts, like other winter squashes, can be eaten immature much like summer squashes. I pick off any winter squashes that I know don't have time to ripen, and steam or saute them.
However, you likely have some squashes that are neither ripe, nor young and tender. Experimentation is in order. Try slicing, cubing, steaming, sauteing, frying, baking or whatever. They are usable, but they don't have the storage endurance of a truly ripe Butternut.

Thanks tcstoehr,
I roasted some that weren't so ripe, and you're right.....they aren't bitter. The puree was VERY thick. I'm thinking these might be good for "pumpkin" pie, since its so thick, and the flavor of those types of pies seem to come mostly from the spices and sugar, rather than the pumpkin/squash.
Thanks for your help.

winter squash/pumpkins continue ripening and changing internally after certain stage. So, they do not need to be on the live or dead vine. The same goes for melons and watermelons. The chemical changes take place continualy, by producing more sugar and loosing moisture.

Thanks cyrus.

I have had acorn squash ripen to a bright orange in the cellar over the winter, when picked slightly early. I have been watching a butternut change from slightly green to tan over the past month, on a shelf in my storage room.

Here is a link that might be useful: My country blog

Thanks sheryl!