Depending how many, you delete all of the scenes, and then the switches from the ISY. Use the set button method to manually link them... that's the complete/sure way.
FWIW I sold my house last summer with the same concern. I left the ISY... removing the more complex integrations. Left a google doc with the basics... brands, logins etc. I created a "house" gmail account that the portal, rainmachine, Venstar thermostats used for their online account; that was turned over with the doc as well.