Was able to delete all primary sysadmins for a system by removing from nested cluster
DILBERT123 had only a single primary sysadmin, no authorized and no cluster membership. I added it to the ALL-FERMIGRID cluster which happened to be contained in the BLOCKWHITELIST cluster.
I then edited the DILBERT123 primary sysadmin to be an authorized admin (legal due to parent cluster having a primary) then I removed DILBERT123 from the ALL-FERMIGRID cluster. This resulted in DILBERT123 having only an authorized admin in Equipdb & Service-now. (When I did the same to DOGBERT123 with a non-nested cluster BLOCKWHITELIST, things worked correctly with the cluster primary getting assigned directly as the system primary.)
#1 Updated by Timothy Zingelman about 6 years ago
Same situation this time using system CATBERT123 but instead of editing the system primary sysadmin to be authorized, I went to the user entry and removed the CATBERT123 system from the administered CIs list, then again removed CATBERT123 from the nested cluster and it resulted in no sysadmins at all for the system in equipdb & service now.