Thanks, guys! Looking at the DAG-2 on the Parktool page (I should have known that 'real' bike mechanics have a tool for fixing anything...) gave me some ideas on how to assess the multiple degrees of twist that this tang of metal has suffered.

I cannot do much with it with an actual rear wheel in place, as the cluster impedes wrench access. Thats why the bare threaded axle. But something that bolts into the hole would provide both grip and leverage, with a reduced risk that it will bend at the hole itself. Worth trying....