Upon trying to install Ubuntu 13.10 x64 in EFI mode on /dev/sda8 over an earlier (also failed) 13.04 64bit partition, I selected the partitioning option:
"Replace existing Ubuntu 13.04 installation"
Thinking that ONLY /dev/sda8 would be wiped, not the entire 500GB disk.
Clearly that was a misunderstanding....a disastrously unclear one, it turned out. Now ALL my other GPT partitions are gone: the OEM Windows 8, all the previous data/programs/user files, system, recovery, boot, 16GB Windows image rollback/restore, boot, EFI, etc.
No more "Windows Bootloader" option after F12 key upon BIOS bootup. Of course, No Ubuntu boot option is present either. Never was, always failed in mid-installation, even with 13.04 and 12.04 64bit versions. (Yet this is a new 6GB AMD laptop with new harddisk, four different USB keys or DVD install disks tested to rule out media failures, etc.)
In Live mode, off a USB key, Gparted only shows three new partitions, automatically made by the Ubuntu installer. The EFI boot area, the Ubuntu main, and swap at end. None of which are important to me in comparison to the old partitions and structure.
Question, How can I roll back to the previous GPT partition table? Where on the disk might be backups stored, and for the previous Windows bootloader too? What could make this recovery process easiest, since I cannot easily remove the harddisk from the laptop, due to the way it's built? Even if 7GB+ of random data might already be damaged.
The short answer: Use your off-disk backups. If you don't have such backups, you now know why you should have them.
The long answer: It's possible that you'll be able to recover some of your partitions with TestDisk or something similar; however, this is far from guaranteed. TestDisk works by looking for the "signatures" of filesystems and creating new partition table entries to match, but these signatures may have been wiped out when Linux was installed -- after all, installing any OS means writing data to the disk, and at least some of that data is likely to overwrite any pre-existing data, thus destroying it. Note the word: destroy. It's precisely accurate. Even if filesystem signatures remain, it's virtually certain that some critical filesystem data structures and/or file contents have been destroyed. If TestDisk fails, or if the recovered partitions are damaged, you may be able to use PhotoRec or something similar to recover some (conceivably even most) of your individual files. This will be a tedious process, though, and you will not be able to recover a bootable Windows system in this way. For that, you'll almost certainly need to acquire a Windows 8 install disc and re-install the OS.
I'm sorry you had to learn it this way, but now you know to keep backups of your critical data.