Q: Home sharing computer to computer drops

You can't share an iTunes library if iTunes isn't running.

I really don't think you are thinking about this properly, it's like expecting your kettle to boil when it's not plugged in.

I'm afraid you are mistaken. They may have been imported (i.e.physically on the computer) but they certainly wouldn't be on via homesharing if iTunes wasn't running on the other computer.

Use Home Sharing to share iTunes content with other devices on your home network - Apple Support

To share or stream content from an iTunes library, make sure that the computer with that library (the host computer) is on and awake, and that iTunes is open.

And Yes, it has ALWAYS worked this way.