I don’t think I’ll ever go back to a previous version, as I never have before (since Cubase 5). But is there any reason I would want to hold onto my dongle? If not, how can I purge it (erase keys) before disposing of it?
Keep it around. You never know if it might come in handy. Plus at some point a working dongle might be kind of valuable. Don’t purge keys unless you actually sell it or something.
Depending on what you own and have stored on it, yes, I would definitely hold onto it for now. Cubase 12 and Dorico 4 are the only Steinberg products that use the new licensing system so any other purchases you’ve made will still require the dongle for now. Also, other vendors still use it for the time being. I still have Arturia, Xils Labs, Eiosis, and VSL on mine.