Solved. used TegraExplorer to dump PRODINFO, got BIS keys with Lockpick_RCM. Rebuilt new raw image from there with Sthetix's guide. If you can only dump PRODINFO via Tegra Explorer due to a corrupt GPT, you'll need to flash it back via Tegra Explorer once you've rebuilt your image, as it dumps it in a decrypted state, but Sthetix's guide "level 2" uses an encrypted PROD. NxNandManager will complain about your keys if it can't read prodinfo, but you're safe to flash it via Hekate as long as you have a raw gpp backup. Then just write PRODINFO back that you dumped earlier. You lose your PRODINFO or BIS keys, your console will never be able to play online again.
