Yesterday's Magic — Pamela F. Service

WHEN HEATHER MCKENNA is kidnapped by the sorceress Morgan LeFay, it is up to Heather's friend Welly and the wizard Merlin (yes, that Merlin), to rescue her. Set 500 years in the future, following a nuclear devastation, the technological world has ground to a halt, but magic is beginning to take hold again. And the powerful icons of myth are starting to fight over control of the world. From the Russian witch Baba Yaga, to the native American trickster god, Raven, the most ancient magical forces are beginning to awaken, and they have very different ideas about the future of the earth.
This riveting sequel to Tomorrow's Magic continues Merlin and Arthur's quest to reunite the world.