You can disable all its callback features. All that's left is the interface to windows search. 9)% of what Cortana is is just a new cross-entity search framework for your stuff. But you can turn it all off by unpairing it (or just using an local Win10 Account).
Or you can keep squatting on Windows 7 until it EOLs and use a desktop OS that manages to be even more dated than Mac OS X.
The fact I have to write a host file to do that makes it rather irritating but, yes, with a local account and the appropriate host file and all the features turned off it sorta-works.
The concern is Windows Update will turn it back on as it has with other things in the past.