I think it would be ok to have a second "Save page" prompt that offers to save the page in a user's userspace.
The save location could be something like User:Jimbo\editconflicts\pagename
Auto-deletion of the edit conflict save would not be necessary.
I also like Zack's suggestion. I think that could work with differences highlighted between the two versions:
"EDIT CONFLICT. Another user has edited the page between the time that you started your edit and the time that you saved the page. But don't worry, you can reconcile the differences."
YOUR VERSION OTHER VERSION +-------------+ +-------------+ | (read only | | (read only | | text area) | | text area) | | (background | | (background | | greenish) | | yellowish) | +-------------+ +-------------+
"Please merge the two versions into the text area below and then press save." +----------------------------- -+ | (editable text area) | | (background white) | | (prefilled with the best | | 3-way merge we can manage) | +------------------------------+
Pine