Hey Shannon, yeah I think this came up a while ago and clients keep wanting this. We built a crude version of it back in 4.0 (something like 3 years ago :)
Here's a high-level use case:
1) User clicks on a node in the content tree
2) System opens node for edit
3) User makes a change to any field (within any tab)
4) User navigates away from the edit view (clicks on a another node, section, or attempts in some way to unload the page)
5) System displays a "Changes have been made to your document. Leave or stay?" (maybe even "Publish" or "Save" or "Discard")
6) User clicks "Stay"
6a) User remains on the page
7) User clicks "Leave"
7a) User is taken to the desired destination (from step 2)
If there is room for other UI help in Belle, let us know and we'll try to help where we can.
Thanks!