This story will require some investigation.
Ideal logic would be: if the Create Page app is installed then disable it AND migrate all existing macros to the new copy we setup in
There should be some feedback to the user to tell them, "Hey, your macros have been migrated. We disabled Create Page, and you can uninstall it."
However, it may not be as straightforward to migrate data and disable the other plugin. The way ScriptRunner for Jira handled this case with the Template Comments for Jira Service Desk plugin was actually the reverse: if the old plugin was installed, they disabled ScriptRunner's module that had the redundant functionality. That was slightly different, though, in that the configuration was stored via ActiveObjects, and could easily be passed between plugins. Migrating macros may be different, as they have their own storage format.