I would take it out, in case it has something contagious. That's just me, though. Then you could look to see what parts were effected and have a better idea of what is wrong. I'm concerned it might be some sort of fungal disease or bacterial blight.
A larva that bores into the vine and eats out a 'cavern' there, which beyond a certain point will interfere with the plant's vascular system and cause all parts of the vine beyond where the borer is to collapse. Look for a hole, or funny-lookin' part of the vine, or area that maybe is looking like it is starting to dry out or rot. On this plant, if it's a borer it's pretty close to the base of the plant where it comes out of the soil. Look closely.
I agree with DrakeMaiden - I'd pull the whole plant out (*then* do a postmortem to try to find its problem) on the grounds that if it's contagious you sure don't want your other squash plants getting it and even if it isn't you're not going to be getting much yield from that particular plant anyhow.