I did try to uninstall using
make uninstall as instructed in the documentation of the software, but that unfortunately did not work.
Trying to troubleshoot the service according to your link did not work either.
Since the snapshots of my rpool are before I configured the zones and services and with the possibility of an existing bug that makes my machine unreachable in 11.3 I have decided to do a clean install of 11.1 and set everything up from the beginning while my memory of it is fairly fresh. I made some configscripts this time when I installed everything which will help me set things up fairly quickly as well.
Even if I manage to fix this with the help of you guys, I won't fully trust it not to happen again. And not least, I need this machine up and running and troubleshooting it takes too long.
Lesson learned: turn on timeslider the first thing you do and be generous with snapshots before doing stuff.
It's just easy to forget those things when 11.1 was rock solid for several years.
Thanks anyways for trying to help me as much as you have.