Post is for anyone qogir who experienced a complete dark theme white-out after update today.
In budgie-desktop-settings, korla was preserved, but the Qogir-dark was missing from the from the Widget box in BDS. It got nudged and default Light theme took over.
In BDS simply switch the blank Widget pull-down entry back to Qogir-dark. All restored. Easy peasey.
edit: typopalooza