So say we posted a bunch of stuff a few months ago to a specific art work thread, then we didnt post for a long time and said thread ends up on like the 4th page. (hypothetically speaking...) then we come back today and post something to that thread, will that thread then be moved to the front page of the section? or will it just stay in the back never to be seen again?

It will be moved to the front. It's called "bumping". It's stretching the rules a little bit if you're replying to something someone said, but it's ok if you're adding new content for other people to talk about.

Bump = Bring Up My Post