I'm thinking Fusarium from what I just googled around?

This is a Blue Hubbard squash. Leaves started turning yellow a couple weeks back.

The crown just came apart with very little force, and other parts of the vine that were "rooted" seem to be similiarly rotting. The closer to the original crown, the more rotted.

The dreaded SVB?

I did slice open the vine and didn't find anything looking like borer grub (I found some small, black bug but he kind of looked like he just crawled up there).

Matt, what I'm seeing is not dissimilar to the damage mine had from SVB. Are those holes in your vine in pics 1 and 3?

Hmmm, I really didn't see a "hole" but they were rotted to such a degree the slightest touch and the vines fell apart there.

If you see my "Rot II" post, I might call that a hole further up on the vine, it's not right at ground level. When I read up on SVB, I read, " The point where a borer enters a stem is marked by a hole with yellow granular or sawdust-like frass exuding from it" and I've never seen anything I'd call sawdust though.

Everything you've got there is the work of the SVB.
The rot is due to the borer killing the vine, which then started decomposing.

You didn't find anything inside the stems because the borer has already left the plant, and it is pupating somewhere in the ground.

The reason you didn't find the borer grubs might be they have already left to pupate.

Well alrighty then

Looks like I've never gotten to the point of SVB problems because the Squash Bugs used to suck the life out of the plants first...now that I have the Squash Bugs under control...