Well, I tried the purge and replace option as described in the link in your last post (HowTo: Revert from grub2 to Legacy Grub or grub to grub2). No joy. Pretty much the same result as my previous attempts.
Got the same request to execute the chroot command from a terminal
Got lots of output as a result, but the last line in that output was different:
E: sub-process /usr/bin/dpkg returned an error code (1)
Quit out of the tool and was informed "No operation was performed" and the state of the machine is apparently unchanged. So...?
If I understand you correctly I could do a clean install of the latest version of Ubuntu and then install either fallback or gnome-panel to get the classic desktop back? If so, I may wind up doing that. I have Ubuntu running on my desktop as well, and the laptop copy is sort of my sacrificial environment for experiments of this sort. Nothing on the laptop is worth worrying about loosing.