Hi Amanda! While you won't be able to copy templates that were created using the Legacy-Second-Generation Editor, those campaigns will still appear on your campaigns page. They will not be deleted, but you will have to create a new template in the Third-Generation editor once Legacy is retired.
Not being able to copy a SUPERIOR template is beyond frustrating. It's horse****. This flushes years of work and makes it vastly more difficult to create what we need to create. I read the "why" and don't care about a few display bugs. Ask your customers, I'm betting the majority are **bleep** at ending access to our legacy work.