I manually copied /etc/hp/hplip.conf from another machine and the hplip-gui stuff all works now.
After having looked around I have no idea why 1) this file is even in libsane-hpaio rather than hplip or hplip-gui, 2) it is not insalled when I purge hplip* and autoremove (thus removing libsane-hpaio), rm -rf /etc/hp/ then reinstall hplip-gui (thus reinsalling libsane-hpaio). There is nothing I can see that would stop this file from being unpacked to /etc/hp in this case. If purge/removal of cups/hplip stuff had just killed all the processes, I probably would not have gone crazy with killall, rm -rf, purging, etc, etc.. just to get rid of a bunch of bad settings and duplicate printers that somehow wound up in my configuration and I couldn't figure out how they were surviving purge AND rm -rf. Not to mention I wouldn't have spent so long on this issue after the fact if the config file that is REQUIRED for hplip-gui components to run wasn't in some OTHER package nobody is ever going to think to purge (its a lib package) when trying to get rid of configs, and if reinstalling said package didn't result in failure to provide said config file when its clearly part of the package and there is no postinst script to prevent it from happening in any way. furthermore hplip does have a postinst script that runs two perl one-liners trying to modify this config file /etc/hp/hplip.conf without being able to assure its even there due to whatever weirdness is going on here. Consider moving the config file into hplip or hplip-gui perhaps, unless there is some conceivable way a user would use libsane-hpaio WITHOUT hplip or hplip-gui and this file is actually required for such usage... because I KNOW its required for hplip-gui and it not being in one of the hplip packages causes confusion and potential for breakage. I consider this issue resolved, and advise the maintainers to reconsider placement of this config file and to have pre/postrm scripts stop hplip utils and such to insure that a apt --purge remove cups* hplip* will result in a pristine system so that reinstalling those packages will result in a default cups/hplip configuration clearing out any bad settings. As of right now you can purge and rm -rf the whole damn system and still have all your bad settings because there is no such check to make sure processes keeping these settings in memory are stopped.. which had me banging my head off a wall for a week trying to figure out why I had a ton of fax/printers in the settings when I only have 1 printer, and why cups would not let me change it, saying unauthorized. There is no reason this should be any diferent than everyhing else in debian, where a --purge or --force-confmiss or such will just clear it all out and give you a working default config.