Also, if you could think of any settings I might be able to fiddle with to get my .blend to be useable again, I would greatly appreciate it. Otherwise I'll be forced to recreate the scene again from scratch.

I can confirm on Win 7 that, when opening your file, there is nothing visible in the Layout workspace when shading is set to wireframe and solid. However, the remaining default workspaces display correctly for me in all for shading modes. I deleted the Layout workspace, and then added a new Layout workspace. Everything appears normal in this workspace for me. See my updated version of your file.

The one setting I did notice that was odd to me, was that you had the viewport set to 550 samples, and rendering set to 4. Perhaps this contributed to the issue?

I can confirm that the send file is showing the issue. But in order to fix this we need to know the how to get to this 'corrupted' state in a reproduceable way. Did you know what you did, just before this issue appeared.
I haven't been able to detect the corruption.

oh, @Jeroen Bakker (jbakker) was quicker... does ALT+B make a difference for you as well?

We just had an online discussion about the viewport clipping and what we want to change.

1. Show the viewport clipping in wireframe draw mode. (We will move the current code to overlay_mode.c so the code will be shared)
2. Automatically turn off viewport clipping when rendering in EEVEE or Cycles.

I can confirm that the new version seems to be working. Thanks, @Evan Wilson (EAW) ! I was also able to fix the issue by starting a new .blend file and just appending the Scene from the previous .blend to the new one.

@Jeroen Bakker (jbakker) I'm afraid I don't know quite what I did before I had this problem. It seemed to happen more or less out of the blue. I think it happened when I was modelling the piece of geometry called "Cube.043".

Also some of the settings such as clipping are strange because I was fiddling around with them arbitrarily trying to fix the issue. Before that everything was basically left at default settings... I can't recall anything else I changed, I was mostly just modelling and doing basic shader and animation work.

As for the low render samples, that was deliberate. I was just using that to get a quick preview render.

@Philipp Oeser (lichtwerk) ALT+B seems to fix the issue as well. It's quite possible I hit that accidentally. I don't know what it does.

Thanks so much for helping, guys!

@Alan Noble (AlanNoble) : see the following links for what to use viewport clipping for:
https://docs.blender.org/manual/en/2.80/editors/3dview/navigate/regions.html#view-clipping-region
https://docs.blender.org/manual/en/2.80/sculpt_paint/brush/introduction.html#the-clipping-region

@Alan Noble (AlanNoble) you can try to load your file with disabled LoadUI option in open screen

@Philipp Oeser (lichtwerk) @dark999 (dark999) Thanks for the tips!